دورة شرح برنامج Autocad

دورة شرح برنامج اتوكاد بداية من الصفر و حتى الوصول الى مرحلة الاحترف.

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Shear and moment diagrams

Density table

تسلسل خطوات تنفيذ المباني

تبدأ عملية تنفيذ المبنى بعد توقيع وتحرير عقد المقاول الذي يتولى مهمة الإنشاء وتنفيذ بنود الأعمال، ويتم تحرير شروط هذا العقد تحت إشراف مهندس نقابي متفرغ.
وتم تقسيم مراحل التنفيذ إلى خمس مراحل أساسية مختلفة يمكن تحديدها كالتالي:

1- المرحلة التحضيرية:
وتشمل تسليم الموقع للمقاول واستكشاف التربة وتطهير المكان والتشوين ووضع الجدول الزمني العام والتفصيلي وعمل الميزانية الشبكية للموقع وتحديد المداخل والمخارج ومواضع التشوين وأماكن المهندسين والعمال وتجهيز الموقع بكافة التوصيلات الفنية اللازمة من إمداد المياه والكهرباء والصرف الصحي اللازم وخلافه.

2- المرحلة الإنشائية:
وتشمل أعمال تخطيط الموقع والأد والحفر والردم والإحلال ونقل الأتربة وصب الخرسانات العادية والمسلحة وبناء الحوائط ووضع الطبقات العازلة تحت الأرض.

3- مرحلة التركيبات:
وتشمل أعمال التشطيبات الخاصة بالبياض الداخلي والبياض الخارجي وتركيبات النجارة والكريتال والألومنيوم والكهرباء والمجاري والتغذية بالمياه والتبليطات والتكسيات وتركيب الوحدات سابقة التجهيز إن وجدت وإنجاز أعمال الرصف والطبقات العازلة لرطوبة والحرارة حتى الأسطح العلوية المطلوبة.

4- مرحلة التشطيبات والتسليم:
وتشمل مرحلة نهو أعمال التشطيب وتضم كشط الأرضيات الخشبية ودهانها أو جلي الأرضيات الموزايكو والرخام ودهانات الحوائط وتركيب خردوات النجارة ونماذج الكريتال الدقيقة والديكورات وجميع لوازم الكهرباء والأجهزة الصيني للحمامات والكروم وخلافه وكسوة الواجهات والحوائط الداخلية من ورق الحائط أو التجليد بالأخشاب أو المعادن أو الزجاج وإنهاء أعمال الزخرفة وتركيب أجهزة تكييف الهواء والتسخين والمصاعد وتنسيق الحدائق الداخلية والخارجية إن وجدت.

5- مرحلة الصيانة والترميمات:
وتشمل صيانة جميع الأعمال التي تتطلب التلميع والتنظيف وحماية المبنى إنشائياً ومعمارياً والمحافظة على سلامة ورونق المبنى لإبقائه في أحسن حالة لأطول مدة.

Roller-Compacted Concrete (RCC)

A Different Kind of Concrete

Roller-compacted concrete, or RCC, takes its name from the construction method used to build it. It's placed with conventional or high-density asphalt paving equipment,then compacted with rollers.

RCC has the same basic ingredient as conventional concrete: cement, water, and aggregates, such as gravel or crushed stone.

But unlike conventional concrete, it's a drier mix—stiff enough to be compacted by vibratory rollers. Typically, RCC is constructed without joints. It needs neither forms nor finishing, nor does it contain dowels or steel reinforcing.

These characteristics make RCC simple, fast, and economical.

Tough, Fast, Economical

These qualities have taken roller-compacted concrete from specialized applications to mainstream pavement. Today, RCC is used for any type of industrial or heavy-duty pavement. The reason is simple. RCC has the strength and performance of conventional concrete with the economy and simplicity of asphalt. Coupled with long service life and minimal maintenance, RCC's low initial cost adds up to economy and value.

Roots in Logging

RCC got its start in the Seventies, when the Canadian logging industry switched to environmentally cleaner, land-based log-sorting methods. The industry needed a strong pavement to stand up to massive loads and specialized equipment. Yet economy was equally important: log-sorting yards can span 40 acres or more. RCC met this challenge and has since expanded to other heavy-duty applications.

Today, RCC is used when strength, durability, and economy are primary needs: Port, intermodal, and military facilities; parking, storage, and staging areas; streets, intersections, and low-speed roads.

No Rutting, No Pot Holes

The high strength of RCC pavements eliminates common and costly problems traditionally associated with asphalt pavements. 
RCC pavements:

• Resist rutting
• Span soft localized subgrades
• Will not deform under heavy, concentrated loads
• Do not deteriorate from spills of fuels and hydraulic fluids
• Will not soften under high temperatures

Unique Mix, Unique Construction

RCC owes much of its economy to high-volume, high-speed construction methods.Large-capacity mixers set the pace. Normally, RCC is blended in continuous-mixing pugmills at or near the construction site. These high-output pugmills have the mixing efficiency needed to evenly disperse the relatively small amount of water used.

Dump trucks transport the RCC and discharge it into an asphalt paver, which places the material in layers up to 10-inches thick and 42-feet wide.

Compaction is the most important stage of construction: it provides density, strength, smoothness, and surface texture. Compaction begins immediately after placement and continues until the pavement meets density requirements.

Curing ensures a strong and durable pavement. As with any type of concrete, curing makes moisture available for hydration—the chemical reaction that causes concrete to harden and gain strength. A water cure sprays or irrigates the pavement to keep it moist. A spray-on membrane can also be used to seal moisture inside.

When appearance is important, joints can be saw cut into the RCC to control crack location. If economy outweighs appearance, the RCC is allowed to crack naturally.

Once cured, the pavement is ready for use. An asphalt surface is sometimes applied for greater smoothness or as a riding surface for high-speed traffic.

Economy. Performance. Versatility.

For RCC, economy was the mother of invention. The need for a low-cost, high-volume material for industrial pavements led to its development.

Low cost continues to draw engineers, owners, and construction managers to RCC. But today's RCC owes much of its appeal to performance: The strength to withstand heavy and specialized loads; the durability to resist freeze-thaw damage; and the versatility to take on a wide variety of paving applications. From container ports to parking lots, RCC is the right choice for tough duty.

Ready Mixed Concrete

Ready mixed refers to concrete that is batched for delivery from a central plant instead of being mixed on the job site. Each batch of ready-mixed concrete is tailor-made according to the specifics of the contractor and is delivered to the contractor in a plastic condition, usually in the cylindrical trucks often known as "cement mixers."

As early as 1909, concrete was delivered by a horse-drawn mixer that used paddles turned by the cart's wheels to mix concrete en route to the jobsite. In 1916, Stephen Stepanian of Columbus, Ohio, developed a self-discharging motorized transit mixer that was the predecessor of the modern ready-mixed concrete truck. Development of improved ready-mixed trucks was hindered by the poor quality of motor trucks in the 1920s. During the 1940s, the availability of heavier trucks and better engines allowed mixing drum capacities to increase, which in turn allowed ready-mixed concrete producers to meet the high demand for concrete caused by World War II. 

Ideal for Many Jobs

Ready-mixed concrete is particularly advantageous when small quantities of concrete or intermittent placing of concrete are required. Ready-mixed concrete is also ideal for large jobs where space is limited and there is little room for a mixing plant and aggregate stockpiles. There are three principal categories of ready mixed concrete: 

• Transit-mixed (also known as truck-mixed) concrete, materials are batched at a central plant and are completely mixed in the truck in transit. Frequently, the concrete is partially mixed in transit and mixing is completed at the jobsite. Transit-mixing keeps the water separate from the cement and aggregates and allows the concrete to be mixed immediately before placement at the construction site. This method avoids the problems of premature hardening and slump loss that result from potential delays in transportation or placement of central-mixed concrete. Additionally, transit-mixing allows concrete to be hauled to construction sites further away from the plant. A disadvantage to transit-mixed concrete, however, is that the truck capacity is smaller than that of the same truck containing central-mixed concrete.

• Shrink-mixed concrete is used to increase the truck's load capacity and retain the advantages of transit-mixed concrete. In shrink-mixed concrete, concrete is partially mixed at the plant to reduce or shrink the volume of the mixture and mixing is completed in transit or at the jobsite.

Ready-mixed concrete is often remixed once it arrives at the jobsite to ensure that the proper slump is obtained. However, concrete that has been remixed tends to set more rapidly than concrete mixed only once. Materials, such as water and some varieties of admixtures, are often added to the concrete at the jobsite after it has been batched to ensure that the specified properties are attained before placement.

Prestressed Concrete

Although prestressed concrete was patented by a San Francisco engineer in 1886, it did not emerge as an accepted building material until a half-century later. The shortage of steel in Europe after World War II coupled with technological advancements in high-strength concrete and steel made prestressed concrete the building material of choice during European post-war reconstruction. North America's first prestressed concrete structure, the Walnut Lane Memorial Bridge in Philadelphia, Pennsylvania, however, was not completed until 1951. 

In conventional reinforced concrete, the high tensile strength of steel is combined with concrete's great compressive strength to form a structural material that is strong in both compression and tension. The principle behind prestressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.

Prestressing removes a number of design limitations conventional concrete places on span and load and permits the building of roofs, floors, bridges, and walls with longer unsupported spans. This allows architects and engineers to design and build lighter and shallower concrete structures without sacrificing strength.

The principle behind prestressing is applied when a row of books is moved from place to place. Instead of stacking the books vertically and carrying them, the books may be moved in a horizontal position by applying pressure to the books at the end of the row. When sufficient pressure is applied, compressive stresses are induced throughout the entire row, and the whole row can be lifted and carried horizontally at once.

Compressive Strength Added

Compressive stresses are induced in prestressed concrete either by pretensioning or post-tensioning the steel reinforcement.

In pretensioning, the steel is stretched before the concrete is placed. High-strength steel tendons are placed between two abutments and stretched to 70 to 80 percent of their ultimate strength. Concrete is poured into molds around the tendons and allowed to cure. Once the concrete reaches the required strength, the stretching forces are released. As the steel reacts to regain its original length, the tensile stresses are translated into a compressive stress in the concrete. Typical products for pretensioned concrete are roof slabs, piles, poles, bridge girders, wall panels, and railroad ties.

In post-tensioning, the steel is stretched after the concrete hardens. Concrete is cast around, but not in contact with unstretched steel. In many cases, ducts are formed in the concrete unit using thin walled steel forms. Once the concrete has hardened to the required strength, the steel tendons are inserted and stretched against the ends of the unit and anchored off externally, placing the concrete into compression. Post-tensioned concrete is used for cast-in-place concrete and for bridges, large girders, floor slabs, shells, roofs, and pavements. 

Prestressed concrete has experienced greatest growth in the field of commercial buildings. For buildings such as shopping centers, prestressed concrete is an ideal choice because it provides the span length necessary for flexibility and alteration of the internal structure. Prestressed concrete is also used in school auditoriums, gymnasiums, and cafeterias because of its acoustical properties and its ability to provide long, open spaces. One of the most widespread uses of prestressed concrete is parking garages.

Precast Concrete

In 1950, the completion of the Walnut Lane Memorial Bridge in Philadelphia, Pennsylvania, signaled the beginning of the precast concrete industry in North America. Virtually unknown in the United States until the construction of this prestressed concrete bridge, today, precast concrete structures, including bridges, are commonplace in the United States.

Precast concrete is widely used in low- and mid-rise apartment buildings, hotels, motels, and nursing homes. The concrete provides superior fire resistance and sound control for the individual units and reduces fire insurance rates.

Precast concrete is also a popular material for constructing office buildings. The walls of the building can be manufactured while the on-site foundations are being built, providing significant time savings and resulting in early occupancy.

The speed and ease with which precast structures can be built has helped make precast a popular building material for parking structures. Precast concrete allows efficient, economical construction in all weather conditions and provides the long clear spans and open spaces needed in parking structures. For stadiums and arenas, seating units and concrete steps can be mass produced according to specifications, providing fast installation and long lasting service. In addition, pedestrian ramps, concession stands, and dressing room areas can all be framed and constructed with precast concrete.

The smooth surfaces produced with precast concrete and the ability of precast, prestressed concrete to span long distances makes precast suitable for use in manufacturing and storage structures. Additional applications for precast concrete include piles and deck for railroad and highway bridges, railway crossties, burial vaults, educational institutions, commercial buildings such as shopping malls, and public buildings including hospitals, libraries, and airport terminals.

A benefit of precast concrete is that the product is created in ideal manufacturing conditions. Although some products are cast outdoors, especially in temperate climates, many precast plants operate indoors where the climate can be fully controlled.

Standard or Special

There are two types of precast products. Standard products such as beams, decks, and railroad ties are shaped in one way and used repeatedly. The other type of product is a specialty product, designed especially for the building, bridge, or structure where it will be used. Most precast companies have their own carpentry shops where skilled workers create forms for the many specialty-precast products available. Architectural concrete is often cast specially for each new project.  

The forms, whether standard or specialty, are well oiled. Concrete is placed in the forms and allowed to cure. After curing, the product is carefully lifted from the form and taken to a yard for further curing before it is shipped to the project site The form is then carefully cleaned and prepared for the next batch of concrete. Many precasters can turn over their forms every one or two days.

Insulating Concrete Forms

Insulating concrete form systems (ICFs) have been successfully used by European and Canadian builders for decades, yet the systems did not make a mark in the United States until the 1990s. This builder-friendly wall system, which is a variation of poured-in-place concrete construction, has found its way into many new homes across every region and in every price range.

In conventional poured-in-place construction, a crew erects forms of plywood, steel, or aluminum that make a mold in the shape of the desired walls. After placing rebar to reinforce the wall, the crew pours concrete inside the cavity. Once the concrete hardens, the crew strips the forms to leave the reinforced concrete walls.

Unlike these removable forms, ICFs are designed to stay in place as a permanent part of the wall assembly. The formwork functions as the insulation and the concrete functions as the structure.

A handful of these systems are manufactured from hybrid combinations of insulating materials, including wood fiber and cement, or plastic foam beads and cement. Far more commonly available are ICFs made with expanded or extruded polystyrene, containing up to 20 percent recycled materials. Expanded polystyrene is formed by expanding plastic beads in a mold and is similar to vending machine coffee cups. Extruded polystyrene is made by expanding plastic resin and extruding through a die and is similar to grocery store meat trays. 

Foam form units typically provide at least two inches  of insulation on both faces of a concrete wall, which can commonly be four to 12 inches thick. The result is a solid assembly with strong thermal properties that holds down energy costs. The integral, permanent insulation allows builders to create super-efficient insulated walls—from an effective R-20 to R-40-in a fraction of the time required with wood or steel frame

The Basics

There are two ways ICFs can arrive on the job: as blocks or planks. The block systems arrive at the site with plastic or metal ties and foam, pre-formed and ready to stack and interlock almost like children's building blocks. Plank systems come as separate panels or planks of foam that are assembled on site with individual ties. The block systems offer labor savings through faster assembly on the site while the plank systems offer savings through more compact shipping.

Within these two basic ICF types, individual systems can vary in the profile of the wall they create. "Flat" systems yield a continuous thickness of concrete, like a conventionally poured wall. The wall produced by "grid" systems has a waffle pattern where the concrete is thicker at some points than others. "Post and beam" systems have just that—discrete horizontal and vertical columns of concrete that are completely encapsulated in foam insulation. Whatever their differences, all major ICF systems are engineer-designed, code-accepted and field-proven.

While the formwork is stacked or assembled vertical and horizontal reinforcement is installed. Then contractors pump concrete into the cavity to create a solid structural wall with insulation on both sides. Once crews complete the wall, electricians cut channels for cables and wires into the forms. Plumbers can work in a similar way, placing cold and hot water lines in the insulation after the concrete is poured. 

The insulation provided by the forms gives builders the ability to successfully place concrete even during extremes of weather. Few weather conditions affect a pour because the form insulates the concrete, allowing it to cure while isolated from outside temperature or humidity. Because of ideal curing conditions created within the forms , the risk of serious cracks developing is diminished. The left-in-place forms provide a continuous insulation and sound barrier.

ICFs can be cut to any shape to allow for unique home designs or site conditions. Because ICFs provide a flat, continuous surface to work on, troweled finishes generally go onto ICFs with little advance preparation. In addition, the ends of the ties themselves are typically designed to accept fasteners to permit interior drywall to be installed directly over the forms. Similarly, this built-in furring permits mechanical attachment of exterior finishes like lath for stucco, furred and direct attached siding, or masonry veneer. There are even brick ledge forms to help further simplify brick installation. 

Currently, ICFs are used to build walls for all types of buildings, and several manufacturers have additional forming components that will allow the construction of attached concrete floors and/or roofs. There are several brands of foam forming systems readily available in almost every region of the country.

High-Strength Concrete

In the early 1970s, experts predicted that the practical limit of ready-mixed concrete would be unlikely to exceed a compressive strength greater than 11,000 pounds square inch (psi). Over the past two decades, the development of high-strength concrete has enabled builders to easily meet and surpass this estimate. Two buildings in Seattle, Washington, contain concrete with a compressive strength of 19,000 psi. 

The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute defines high-strength concrete as concrete with a compressive strength greater than 6,000 psi. 

Likewise, there is not a precise point of separation between high-strength concrete and ultra-high performance concrete, which has greater compressive strength than high-strength concrete and other superior properties. See ultra high-performance concrete.

Manufacture of high-strength concrete involves making optimal use of the basic ingredients that constitute normal-strength concrete. Producers of high-strength concrete know what factors affect compressive strength and know how to manipulate those factors to achieve the required strength. In addition to selecting a high-quality portland cement, producers optimize aggregates, then optimize the combination of materials by varying the proportions of cement, water, aggregates, and admixtures.

When selecting aggregates for high-strength concrete, producers consider the strength of the aggregate, the optimum size of the aggregate, the bond between the cement paste and the aggregate, and the surface characteristics of the aggregate. Any of these properties could limit the ultimate strength of high-strength concrete.

Admixtures

Pozzolans, such as fly ash and silica fume, are the most commonly used mineral admixtures in high-strength concrete. These materials impart additional strength to the concrete by reacting with portland cement hydration products to create additional C-S-H gel, the part of the paste responsible for concrete strength.

It would be difficult to produce high-strength concrete mixtures without using chemical admixtures. A common practice is to use a superplasticizer in combination with a water-reducing retarder. The superplasticizer gives the concrete adequate workability at low water-cement ratios, leading to concrete with greater strength. The water-reducing retarder slows the hydration of the cement and allows workers more time to place the concrete.

High-strength concrete is specified where reduced weight is important or where architectural considerations call for small support elements. By carrying loads more efficiently than normal-strength concrete, high-strength concrete also reduces the total amount of material placed and lowers the overall cost of the structure.

The most common use of high-strength concrete is for construction of high-rise buildings. At 969 feet, Chicago's 311 South Wacker Drive uses concrete with compressive strengths up to 12,000 psi and is one of the tallest concrete buildings in the United States.

Focus on Floors

The following sections will help you through the various issues relating to concrete slabs and floors (click on topic). You will find that there is much more than you imagined to that hard surface you walk on every day.

Concrete Floors and Moisture

Issues relating to moisture have been known to cause problems when using moisture sensitive floor coverings. However, with the proper materials, procedures, and workmanship, concrete floors can be constructed to provide years of quality service. Understanding how concrete floors and floor coverings can be protected from moisture exposure can help prevent troubles from arising.

Concrete Shrinkage

The shrinkage of a concrete mixture can have a significant impact on the performance of floors on ground. Knowledge of potential concrete shrinkage can help minimize many problems.

Decorative Floors

Decorative concrete floors have seen no bounds as the creativity of artists and concrete contractors have crossed paths. Through the use of stains, stamps, dyes, colored pigments, textured patterns, ornate sawcuts, epoxied overlays, and more, concrete floors are becoming increasingly attractive for home and facility owners

Durable Floors

Durable concrete slabs begin with quality materials, good design, and proper workmanship. Beyond these essentials, measures can be taken to ensure your concrete slab is protected from the elements.

Elevated Slabs-Concrete Floor Systems

Elevated concrete slabs and concrete floor systems offer a myriad of choices for architects and engineers in the building construction markets. Resources, design examples, reference materials, and design software products are available to facilitate incorporating concrete floors in achieving economy and durability in today’s buildings.

Industrial Floors

Concrete slabs on grade can be found in nearly every single industrial and commercial building. Whether they exist below a layer of floor covering or are exposed, slabs on grade provide foundation for all building structures

Radiant-Heated Floors

Concrete slabs not only provide a durable and decorative interior flooring surface, they can also serve as a giant radiant heat source. Called hydronic heating systems, radiant-heated floors employ tubes embedded in concrete and circulate warm water throughout the building.

Controlled Low-Strength Material

In 1964, the U.S. Bureau of Reclamation documented the first known use of controlled low-strength material (CLSM). Plastic soil-cement, as the Bureau called it, was used as pipe bedding on over 320 miles of the Canadian River Aqueduct Project in northwestern Texas. Since 1964, CLSM has become a popular material for projects such as structural fill, foundation support, pavement base, and conduit bedding.

CLSM is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted backfill. Several terms are currently used to describe this material, including flowable fill, controlled density fill, flowable mortar, plastic soil-cement, soil-cement slurry, K-Krete, and other names. CLSM is defined as a material that results in a compressive strength of 1,200 pounds per square inch (psi) or less. Most current CLSM applications require unconfined compressive strengths of 200 psi or less. This lower strength requirement is necessary to allow for future excavation of CLSM.

The term CLSM can be used to describe a family of mixtures for a variety of applications. For example, the upper limit of 1,200 psi allows use of this material for applications where future excavation is unlikely, such as structural fill under buildings. Low density CLSM describes a material with distinctive properties and mixing procedures. Future CLSM mixtures may be developed as anticorrosion fills, thermal fills, and durable pavement bases.

CLSM is composed of water, portland cement, aggregate, and fly ash. It is a fluid material with typical slumps of 10 inches or more. It has the consistency of a milk shake.

Fast Discharge

Like most concrete, CLSM may be mixed in central-mix concrete plants, ready-mixed concrete trucks or pugmills. Once CLSM is transported to the jobsite, the mixture may be placed using chutes, conveyors, buckets, or pumps depending upon the application and its accessibility. A truck often can be discharged in less than five minutes. A constant supply of CLSM will keep the material flowing and will make it flow horizontal distances of 300 feet or more. Although CLSM may be placed continuously in most applications, care must be taken when backfilling around pipes. For pipe bedding and backfilling, CLSM is placed in lifts to prevent the pipes from floating. Internal vibration or compaction is not needed to consolidate CLSM mixtures. Its fluidity is sufficient to consolidate under its own weight.

The fluidity/flowability and self-compacting properties of CLSM mixtures make CLSM an economical alternative to compacted granular material due to savings of labor and time during placing. CLSM is also an all-weather construction material—it will displace any standing water left in a trench—making it a ideal material for many projects.

The primary application of CLSM is as structural fill or backfill in place of compacted soil. The flowable characteristics of CLSM mean that it can readily be placed into a trench and into tight or restricted-access areas where placing and compacting fill is difficult. CLSM also makes an excellent bedding material for pipe, electrical, telephone, and other types of conduits because the mixture easily fills voids beneath the conduit and provides uniform support.

CLSM will not settle or rut under loads, making the material an ideal pavement base. Additionally, CLSM can be placed quickly and support traffic load within hours of placement-minimizing repair time and allowing a rapid return to traffic. CLSM may be equal to or less than the cost of using standard compacted backfill.

Since 1979, the Iowa Department of Transportation has used CLSM to structurally modify more than 40 substandard bridges by converting them into culverts. CLSM is also used to fill large voids such as old tunnels and sewers. In a Milwaukee project, 830 cubic yards of CLSM were used to fill an abandoned tunnel.

A ready-mixed concrete producer can aid in developing a mix design for CLSM. However, when ordering CLSM, consider the following:

Strength: Applications that require removal of CLSM at a later date usually limit the maximum compressive strength to less than 200 psi.

Setting and Early Strength: Hardening time can be as short as one hour, but can take up to 8 hours depending on mix design and trench conditions.

Density in Place: Density of normal CLSM in place typically ranges from 90 to 125 pounds per cubic foot.

Flowability: Flowability can be enhanced through the use of fly ash or air entrainment.

Durability: CLSM materials are not designed to resist freezing and thawing, abrasive or erosive actions, or aggressive chemicals.

Concrete Pipe

Concrete pipe has a well established history and reputation for being a long lasting, serviceable material. The Cloacae Maxima, built in about 180 B.C. as part of Rome's main sewer system, was constructed mainly of stone masonry and natural cement concrete. More than 2,000 years later, portions of the concrete sewer are still in use.

Modern day concrete pipe sewer systems emerged during the mid-19th century when the public became conscious of the need for sanitation to control the spread of disease. The earliest recorded use of concrete pipe in the United States is a sewer installation built in 1842 at Mohawk, N.Y. Other New England cities followed suit and installed concrete pipelines in the second half of the nineteenth century. Many of these concrete pipelines are still in use today.

Milestones in concrete pipe development include the production of the first reinforced concrete pipe in 1905, the invention of prestressed concrete pipe in the 1930s, and the manufacture of the first steel-cylinder prestressed concrete pipe in 1942. 

Concrete pipe comes in many shapes and sizes. Concrete pipe sizes can range from four inches up to 17 feet in diameter. Although concrete pipe can be manufactured in a variety of shapes, there are five standard shapes: circular, horizontal elliptical, vertical elliptical, arch, and rectangular. The pipe shape selected for a project depends on the topography of the site, importance of hydraulic and structural efficiency, erosion and deposition in the stream channel, and cost. Most often, the preferred pipe shape is the one that will alter the natural drainage flow the least.

Five Methods of Producing Concrete Pipe

As with all concrete products, the basic materials of concrete pipe are portland cement, aggregate, and water. There are five basic methods of producing concrete pipe. Four methods -- centrifugal/spinning, dry cast, packerhead, and tamp-entail using a dry concrete mix. The fifth method, wet casting, uses a high-slump concrete mix. Wet-cast concrete mix usually has a slump less than four inches and is most frequently used for manufacturing large diameter pipe.

Concrete pipe serves as a conduit material for irrigation, water supply lines, sanitary sewers, culverts, and storm drains. Culverts, usually made with arch-shaped concrete, are used to carry water under highways in non-urban areas. Storm drain systems for cities and towns are becoming more important as communities become larger and more densely populated. Recent major floods and the resulting damage only emphasize the need for efficient drainage systems.

Subsurface drainage carries away water below the surface of the pavement. This water reduces flow support capacity of the base and subgrade material causing potential damage to roads, airport runways, and building foundations. Many farm fields depend on proper underground drainage for their cultivation. Thousands of square miles of otherwise arid land rely on concrete irrigation pipe to supply water for farmland. Additionally, most of the large cities in the United States a concrete pipe system to transport their water supply.

Concrete Pavement

Since the first strip of concrete pavement was completed in 1893, concrete has been used extensively for paving highways and airports as well as business and residential streets. There are four types of concrete pavement:

• Plain pavements with dowels that use dowels to provide load transfer and prevent faulting,
• Plain pavements without dowels, in which aggregate interlock transfers loads across joints and prevents faulting,
• Conventionally reinforced pavements that contain steel reinforcement and use dowels in contraction joints, and
• Continuously reinforced pavements that have no contraction joints and are reinforced with continuous longitudinal steel.

To prepare for paving, the subgrade—the native soil on which the pavement is built—must be graded and compacted. Preparation of the subgrade is often followed by the placing of a subbase—a layer of material that lies immediately below the concrete. The essential function of the subbase is to prevent the displacement of soil from underneath the pavement. Subbases may be constructed of granular materials, cement-treated materials, lean concrete, or open-graded, highly-permeable materials, stabilized or unstabilized. Once the subbase has hardened sufficiently to resist marring or distortion by construction traffic, dowels, tiebars, or reinforcing steel are placed and properly aligned in preparation for paving.

There are two methods for paving with concrete—slipform and fixed form. In slipform paving, a machine rides on treads over the area to be paved—similar to a train moving on a set of tracks. Fresh concrete is deposited in front of the paving machine which then spreads, shapes, consolidates, screeds, and float finishes the concrete in one continuous operation. This operation requires close coordination between the concrete placement and the forward speed of the paver.

In fixed-form paving, stationary metal forms are set and aligned on a solid foundation and staked rigidly. Final preparation and shaping of the subgrade or subbase is completed after the forms are set. Forms are cleaned and oiled first to ensure that they release from the concrete after the concrete hardens. Once concrete is deposited near its final position on the subgrade, spreading is completed by a mechanical spreader riding on top of the preset forms and the concrete. The spreading machine is followed by one or more machines that shape, consolidate, and float finish the concrete. After the concrete has reached a required strength, the forms are removed and curing of the edges begins immediately. 

Joints Control Cracking

After placing and finishing concrete pavement, joints are created to control cracking and to provide relief for concrete expansion caused by temperature and moisture changes. Joints are normally created by sawing.

Once joints have been inserted, the surface must be textured. To obtain the desired amount of skid resistance, texturing should be done just after the water sheen has disappeared and just before the concrete becomes non-plastic. Texturing is done using burlap drag, artificial-turf drag, wire brooming, grooving the plastic concrete with a roller or comb equipped with steel tines, or a combination of these methods.

The chosen method of texturing depends on the environment, and the speed and density of expected traffic. Curing begins immediately after finishing operations and as soon as the surface will not be marred by the curing medium. Common curing methods include using white pigmented liquid membrane curing compounds. Occasionally, curing is accomplished by waterproof paper or plastic covers such as polyethylene sheets, or wet cotton mats or burlap.

As the concrete pavement hardens, it contracts and cracks. If the contraction joints have been correctly designed and constructed, the cracks will occur below the joints. As the concrete continues to contract, the joints will open-providing room for the concrete to expand in hot weather and in moist conditions. Once the pavement hardens, the joints are cleaned and sealed to exclude foreign material that would be damaging to the concrete when it expands. The pavement is opened to traffic after the specified curing period and when tests indicate that the concrete has reached the required strength. Immediately before the pavement is opened to public traffic, the shoulders are finished and the pavement is cleaned.

Concrete Masonry Units

Concrete masonry systems (CMS) are familiar to most people because they have been used for such a long time. All types of low-rise buildings are made with these materials, from residential to educational to commercial and industrial. The tough exterior of exposed units provides a durable finish in demanding environments. And architects often prefer the aesthetic appeal of masonry to many other finishes.

Concrete masonry units are manufactured from very dry, stiff concrete mixtures. The “no-slump” or “low-slump” material is placed into molds, vibrated and compacted, and demolded quickly. Units are stiff enough to hold their shape as they enter the curing chamber. Afterwards, they are palletized and readied for shipping. Factories through the country manufactured concrete masonry units, adding to local economies and meeting sustainable criteria for availability.

Overview and History

During the past 100 years, manufacture of concrete masonry units (CMU) transitioned from a hand cast process to a highly automated one. Single molds compacted by hand gave way to ganged molds that travel on assembly lines in high-tech manufacturing facilities. These changes have also led to excellent quality control and uniformity of units.

Concrete masonry units are manufactured from very dry, stiff concrete mixtures. The “no-slump” or “low-slump” material is placed into molds, vibrated and compacted, and demolded quickly. Units are stiff enough to hold their shape as they enter the curing chamber. Afterwards, they are palletized and readied for shipping. They are manufactured throughout the country, adding to local economies and meeting sustainable criteria for availability.

Advantages

It’s hard to determine which attribute of CMU is its best. It may vary from one project to another. Certainly, the fact that these are non-combustible is very important. They are durable and long lasting, can provide an attractive finish, can be reinforced as needed to meet demanding structural applications, can contain recycled materials, do not require painting or other treatment, contain no volatile organic compounds (VOCs) or other potentially harmful offgassing materials, and provide thermal mass to maintain uniform temperatures.

From a construction perspective, a nice feature of masonry is that it can be built without much space for staging the construction. On constricted sites or between buildings, this is helpful. It may be more labor intensive than some other concrete construction, but materials are literally available off the shelf and this is advantageous because there is less chance for time delays waiting for special orders.

Sizes, Components, Configurations, Systems

CMU are modular. The most common size is a nominal 8-by-8-by-16- inches. Door and window openings are positioned to minimize cutting of units. Walls that contain one vertical layer of units are called single wythe and two layers are double wythe. It is most common to build single- or double-wythe walls. When wythes are separated by a continuous vertical space, the assembly is known as a cavity wall. Units are held together by mortar.

Reinforcement is placed into horizontal and vertical cavities as needed, with grout placed around it. This helps walls to carry loads and resist other forces acting on them.

Insulation may be added to interior or exterior faces, between wythes, or inside special unit cavities. The benefit of keeping the insulation inside the wall is that the masonry faces are quite durable. Other accessories may be needed to promote proper drainage, attach finishes, and otherwise complete the wall.

Installation, Connections, Finishes

Masonry is laid by skilled masons. They place mortar between units to tie them together. Masonry requires little machinery for placement: a mason and a trowel are the two main things necessary.

Walls, within and between them, are tied together with reinforcement. Joint reinforcement may be used along mortar joints to help control cracking in the wall. Anchors, plates, and other items that are common with other construction are used in masonry, too.

Finishes are often simplified when using masonry. It can be sealed or painted. It can be plastered for aesthetics and improved moisture resistance. But in many cases, it is left exposed. This can be done with plain or architectural units. Some finishes are made specifically for durability in moist exposures, like locker rooms, pools, or kitchen or laundry facilities. These masonry surfaces are often brightly colored to provide a hard, attractive finish.

Sustainability and Energy

Concrete masonry is sustainable for a number of reasons. It can contain recycled materials. It is made from local materials and usually shipped short distances to a project. These aspects often contribute toward credits in green rating systems.

Masonry construction is energy efficient, providing thermal mass to help moderate temperature in buildings. Lighter weight units are made with lightweight aggregate to help provide added thermal resistance. In addition, masonry walls can be insulated in a wide variety of ways.

Building Codes

Masonry has its own code requirements. A Code and Specification jointly published by The Masonry Society, American Concrete Institute, and the Structural Engineering Institute of the American Society of Civil Engineers are written as legal documents so that they may be adopted by reference in general building codes. They address materials, labor, design, and construction.

Concrete Masonry Projects

Concrete Masonry Affords Opportunities for Building Green on Infill Sites

Infill sites are neglected public spaces and clusters of vacant or nearly-empty buildings and land in either urban or suburban communities. Concrete masonry units (CMU) are an ideal building material for infill projects because there is often no adjacent space available for large equipment or staging areas. And because these projects tend to be tall, thin, and closely situated to property lines, the inherent strength, fire resistance, and noise abatement of CMUs provide an economical solution.

One recent infill project is an eco-friendly residence in southern California. It has a small carbon footprint in balance with lifestyle common in the area, but functions as a high-performance building.

Twenhofel Middle School: Benefits Add Up in Classroom Settings

Located near Cincinnati, Twenhofel Middle School was one of Kentucky’s first schools to incorporate sustainable building principles and energy conservation measures. In 2004, these ideas were not necessarily revolutionary, but neither had they been the focus of school administrators prior to that time. The excellent results achieved with Twenhofel have only increased the district’s efforts to do more of the same.

The backbone of this school is concrete masonry. Generally, one reason concrete masonry has been so popular in schools is its durability. Hard surfaces stand up to wear and tear that is so common in schools and other high usage areas. The walls of Twenhofel are double-wythe masonry, consisting of CMU backup and an exterior clay brick finish with 1½ inches of insulation in between for an R-15 rating. Like most walls with thermal mass, these masonry sections perform better than their apparent R-value. This construction, along with many other energy-efficient features, results in 31 percent less energy usage than an average Kentucky school. That’s good for the environment and is a direct savings to the school’s bottom line.

Beyond the energy efficient envelope, this school is designed with a whole array of features that focus on performance. There is a geothermal HVAC system, increased glazing to improve daylighting and minimize artificial lighting, collection of solar power via a photovoltaic system, and reduced water usage.

Benefits of building high performance schools include:

• Better student performance

• Increased average daily attendance

• Increased teacher satisfaction and retention

• Reduced energy and operating costs

• Positive influence on the environment

As one of the first schools in Kentucky to accomplish these achievements, Twenhofel has been a model and a learning tool. The building itself has monitors and transparent panels as a way to place a focus on building operations and teach about sustainability and energy efficient design and operation. The ability to use the facility as a teaching tool encourages conservation among occupants, teachers, administrators, and students alike.

Concrete Countertops

More and more people are realizing concrete’s value for making countertops. Shapes of concrete countertops are only limited by imagination and the ability to build the forms. With the use of color pigments in combination with white cement and various aggregates, the spectrum of colors available in concrete countertops is virtually limitless.

It’s been more than a decade since concrete countertops found their way into shops, restaurants, and homes. Once the realm of either the do-it-yourselfer or the wealthy, they have gained acceptance in just about every level of residential application, from moderately priced homes to high-end palaces.

Whether an interior is traditional, contemporary, or somewhere between, concrete is a versatile medium to express the aesthetic of designer and owner.

Materials Used in Concrete Countertops

AggregateCoarse and fine aggregate account for the greatest proportions of concrete. Designers should choose aggregate carefully as it can impact the desired final look of the countertop. For example, coarse aggregate may be exposed by grinding or polishing, similar to terrazzo. When that is done, it’s important to get the right size, shape, and color of aggregate particle. From a color perspective, fine aggregate has a greater effect, at least on the mortar portion of the concrete mixture. Smaller particles have a tinting effect on concrete, so the sand can impart an overall hue to the finished surface.

BindersPortland cement binders are the backbone of concrete. These materials glue all the other ingredients into a solid mass. Normal portland cements have a grayish color, although that varies somewhat from one source to another, and perhaps even from one batch to another. For darker colors and untinted concrete, gray portland cements are the easiest choice.

For white or lighter colored surfaces, white portland cement is available. It provides a base that is easily colored with pigments, stains, tints, or dyes. It is a type of portland cement and has the same behavior as its gray counterpart. Here again, sand can play an important role. When mixed with white cement, sand particles impart an overall color to the concrete. If pure white colors are desired, white sand should be used. For other colors, sand should be compatible with the intended color.

Inlays and ImprintsCountertop designers have experimented with various techniques to add interest to surfaces. Inlaid materials include shells, fossils, metal objects and scraps, natural stone, tiles, and other varied pieces. The long-term durability of the inlay should be considered when choosing it, although a sealer will normally provide some additional protection.

Imprints sometimes work in countertops, but shouldn’t be so deep that they pose a collection area for solids or liquids.

FinishesThe most common finish on concrete countertops is a hard steel troweled surface. Not only does this densify the skin, it smooths out the surface so that it is safe for anything that might be placed on it.

PigmentsConcrete pigments come in various forms. For integral coloring, many are based on synthetic mineral oxides for their durability and consistent quality. The liquid versions are the easiest to use because they disperse readily when mixed into the fresh concrete. Powder versions have a long history of use, however, and give excellent results.

Post-applied color is achievable with stains, tints, or dyes. The basic types of materials are chemically reactive stains and water or solvent-based dyes and tints.

Chemical stains are water-based acidic solutions. They contain metallic salts that react with calcium hydroxide in the paste to produce insoluble colored compounds of blue-green, black, brown, or gold. The stain reacts with the concrete with a degree of variation, and can result in a non-uniform effect. They can be used on old or new concrete. Stain also reacts with calcium-based aggregates such as limestone. Stains should be avoided with lean concrete mixtures with low cement content. Prior to staining, concrete should age at least 14 days; blue, green, and gold colors require 30 to 60 days of curing.

Dyes and tints do not react chemically with concrete. They often produce colors that are not available in chemically reactive stains, namely the reds and yellows. They help intensify colors when used in successive applications or can soften or even out the appearance of slabs that have been chemically stained. They are water or solvent-based materials and must be applied to concrete that accepts penetration of materials. The slab should be treated with a degreaser and a mineral acid solution to reach a surface pH of about seven or eight days before dyes and tints are applied. A sealer helps protect the color.

Some manufacturers formulate waxes to work with many of the colored concrete finishes. They can heighten the slab’s color but would have to be deemed safe for food. They improve concrete appearance and help a colored slab retain that appearance, but require periodic reapplication.

SealersIn the past, recommendations were to do periodic maintenance on concrete countertops, but the newer sealers have lessened the need for this activity. One of the most important considerations regarding sealers is the finish. Much like everyday paints, sealers come in glossy, satin, matte, or flat finishes. This aspect of surface treatment has a big impact on the countertop’s appearance. The decision should be made with regard to planned lighting for the space. An article by the Concrete Countertop Institute gives a detailed description of the types available and a comparison of their performance characteristics.

Sinks

Sinks in homes are kitchen necessities but ones that can add interest to countertops. The sink can be concrete, either integrally cast with the countertop or a separate casting, or it can be metal, porcelain, or composite.

Autoclaved Cellular Concrete

Developed in Sweden in the late 1920s, autoclaved cellular concrete (ACC) is a lightweight precast concrete building material that is cured under elevated pressure inside special kilns called autoclaves. Though ACC has been used successfully throughout most of the world since the end of World War II, ACC made a mark in the United States only recently.

ACC, sometimes known as autoclaved aerated concrete, is made with all fine materials-nothing coarser than finely ground sand. What makes ACC different from lightweight aggregate concrete is that ACC contains millions of microscopic cells that are generated during the manufacturing process. In addition, ACC is unlike many other concrete products because it may be drilled, sawed, chiseled, nailed, or screwed using conventional carpentry tools.

Several Formulas

Although several formulas are used for manufacturing ACC, the basic raw materials are portland cement, limestone, aluminum powder, water, and a large proportion of a silica-rich material-usually sand or fly ash. Once raw materials are mixed into a slurry and poured into greased molds, the aluminum powder reacts chemically to create millions of tiny hydrogen gas bubbles. These microscopic, unconnected cells cause the material to expand to nearly twice its original volume—similar to the rising of bread dough—imparting the lightweight cellular quality to ACC. After a setting time ranging from 30 minutes to four hours, the foam-like material is hard enough to be wire cut into the desired shapes and moved into an autoclave for curing.

The autoclave uses high-pressure steam at temperatures of about 356 degrees Fahrenheit to accelerate the hydration of the concrete and spur a second chemical reaction that gives ACC its strength, rigidity, and dimensional stability. Autoclaving can produce in eight to 14 hours concrete strengths equal to strengths obtained in a concrete moist-cured for 28 days at 70 degrees Fahrenheit. The final products are usually shrink wrapped in plastic and transported directly to the construction site.

ACC, which is about one-fourth of the weight of conventional concrete, is available in blocks, wall and roof panels, lintels, and floor slabs. Each of these products can be manufactured in a range of sizes depending on specific applications, allowing for maximum efficiency and flexibility in construction. ACC can be used for all types of structures ranging from single-family housing to large industrial complexes.

ACC is an inert, nontoxic substance that has an energy-efficient and pollution-free manufacturing process. Perhaps the most significant environmental benefit of using ACC is that fly ash can be used as the silica-rich component. The electric utility industry generates more than 50 million tons of fly ash each year—only a fraction of which can be recycled.

ACC is reasonably frost and sulfate resistant, allowing it to be used around the world in all climatic zones and for a wide range of applications. When it is used on the exterior, ACC is normally protected by stucco or other protective coatings. ACC also is an inorganic material, making it 100 percent termite and vermin proof and resistant to rotting and mold.

Architectural & Decorative Concrete

Concrete is one of the most widely used construction materials in the world. One special subset is called architectural and decorative concrete, which refers to a substance that provides an aesthetic finish and structural capabilities in one. This material is made to be seen. Whether creating broad expanses or minute details, concrete permanently captures the chosen look. Achieving an architectural or decorative appearance usually requires that something different be done to the concrete. Whether that involves special forms, special finishing techniques, or special ingredients, the variety of effects is almost unlimited. 

White Portland Cement: A Key Ingredient

White cement concrete is a brilliant architectural material. Whether plain or pigmented, it allows for a broad spectrum of colors - from bright whites and pastels to saturated colors. It can be textured, patterned, or shaped to almost any form, allowing architects to be truly creative in their designs. Imagination becomes architectural reality with white cement.

What makes white cement so architecturally appealing is its versatility. It can be used for:

• Cast-in-place concrete
• Precast concrete
• Tilt-up concrete
• Repair and retrofit applications
• Masonry and mortar
• Stucco finishes
  

Good Looks and More

From large to small items, structural to decorative members, white cement is the key to good looking concrete and masonry construction. A versatile appearance allows white cement concrete, which is pigment-friendly, to fit in with any environment. Beyond aesthetics, its light color offers energy efficiency and safety.

These qualities can be used to advantage for:

• Bridge parapets and barrier medians                                      
• Light reflective floors
• Exposed architectural concrete
• City streetscapes: curbs, gutters and planters
• Landscaping
• Building accents

Whether inside or outside, white cement concrete provides a hard-wearing, durable surface that stands up to heavy use.

Technical Aspects of Designing with White Cement Concrete

White portland cement has essentially the same properties as gray cement, except for its color. An important quality control issue in the industry, the color of white cement depends on raw materials and the manufacturing process. Metal oxides, primarily iron and manganese, influence the whiteness and undertone of the material. White cement is manufactured to conform to ASTM C 150, Specification for Portland Cement. Types I and III are the most common, but Types II and V are also produced.

Mix designs for white or colored concrete are formulated with respect to the following ingredients, paying particular attention to the resultant effect on color:

• Type and color of cement
• Type and dosage of pigment
• Type and dosage of chemical admixtures
• Type, gradation, color, and cleanliness of fine and coarse aggregates
• Type and dosage of supplementary cementing materials: calcined clay, slag, white silica fume
• Consistent proportions, especially maintaining a uniform water-cement ratio

It is always recommended to develop a mix design and build sample panels in advance of starting a white cement concrete project. That way, mixtures can be refined and improved and material usage can be optimized. The mockups serve as references for color and surface appearance during the construction phase of the project.

In North America, white cement is widely available and aggregates are abundant throughout the country. In the end, no matter where you need it, white cement concrete can be there.