Concrete Uses Cement as a Binder

When aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts chemically with the water and other ingredients to form a hard matrix that binds the materials together into a durable stone-like material that has many uses.

Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.

The size distribution of the aggregate determines how much binder is required. 

Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as pasting the surfaces of the aggregate together, and is typically the most expensive component. 

Workability of concrete is an important property of concrete while concrete is in its fresh state. Therefore slump test or compaction factor test should be performed to check workability of concrete. 

Concrete strength is normally to be ascertained from cubes or prisms samples tested at 28 days.

The water permeability test, Rapid Chloride Ion Penetration test, water absorption test, and the initial surface absorption test are tests to determine the durability of concrete. To determine its ability to resist weathering action, chemical attack and any process of deterioration.

Admixture and Surfactant

An admixture is defined as “a material other than water, aggregates, cement and fiber reinforcement that is used as an ingredient of a cement mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing,” and a chemical admixture is defined as “an admixture in the form of a liquid, suspension, or water-soluble solid”.

Many chemical admixtures, such as air-entraining, water-reducing, and shrinkage-reducing, belong to a class of chemicals called surfactants. 

Surfactants have an amphiphilic molecular structure. An amphiphilic is a chemical compound possessing both hydrophilic (water-loving, polar) and hydrophobic (fat-loving) properties. The surfactant hydrophilic area of the molecule penetrates into the polar liquid and the surfactant hydrophobic part into the gas phase. Consequently, the surfactant lowers the surface tension and stabilize air in the form of foam.

Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.

Most commonly, surfactants are classified according to polar head group. A non-ionic surfactant has no charged groups in its head. The head of an ionic surfactant carries a net positive, or negative charge. If the charge is negative, the surfactant is more specifically called anionic; if the charge is positive, it is called cationic. If a surfactant contains a head with two oppositely charged groups, it is termed zwitterionic.

Efflorescence in Cementitious Materials

Efflorescences can occur in natural and built environments. On porous construction materials it may present a cosmetic outer problem only (primary efflorescence causing staining), but can sometimes indicate internal structural weakness (migration/degradation of component materials). Efflorescence occurs when dissolved salts migrate within a porous material to its surface, where the water evaporates and salt precipitate, leaving white spots. Typical efflorescence in materials based on Portland cement (OPC) is caused by calcium carbonate.

Primary efflorescence

This occurs days or weeks after application, during the setting and curing process. Either excess water from the mortar matrix or severe climatic conditions (low temperature, high humidity) extend the setting time and increase the amount of moisture at the surface. The moisture at the surface then reacts with the free lime in the mortar.

For controlling primary efflorescence, formulations containing liquid fatty acid mixtures (e.g., oleic acid and linoleic acid) have been commonly used.

Secondary efflorescence

This can occur years after application due to contact with moisture or when a substrate is subjected to cycles of re-wetting and drying. Moisture penetrates into the matrix and/or leaches substances from it. Calcium hydroxide (a by-product of portland cement) can partly dissolve, or salts (from the substrate) can migrate to the surface.

For controlling secondary efflorescence, admixtures containing aqueous-based calcium stearatedispersion (CSD) are often added at a later stage of the batching process with the mix water.

To prevent (both primary and secondary) efflorescence in cementitious materials is by using special admixtures that chemically react with and bind the salt-based impurities in the concrete.

Ceramic Stain Resistance

Ceramic tiles offer a combination of durability, versatility and convenience and are available in hundreds of different styles, shapes and colors.

Tile is a ceramic surfacing unit, usually relatively thin in relation to facial area, made from clay or a mixture of clay and other ceramic materials, called the body of the tile, having either a “glazed” or “unglazed” face and fired above red heat in the course of manufacture to a temperature sufficiently high to produce specific physical properties and characteristics.

special-purpose tile is a tile, either glazed or unglazed, made to meet or to have specific physical design or appearance characteristics such as size, thickness, shape, color, or decoration; keys or lugs on backs or sides; special resistance to staining, frost, alkalies, acids, thermal shock, physical impact, high coefficient of friction, or electrical properties.

(According to ISO 10545-2) Method applicable to all working surfaces of ceramic tiles to determine their resistance to stains. Each staining agent  (Green staining in light oil/red staining for green tiles,  Iodine alcohol solution, Olive oil) must remain on at least 5 testing samples (whose proper surface has first been cleaned and dried) use of different cleaning agents, for at least 24 hours, whose working surfaces has been cleaned and dried beforehand. Removal of the staining agents takes place in subsequent steps using various cleaning agents and cleaning procedures.

Classification of the results follows visual inspection: class 1 tiles are the easiest from which to remove a given stain, while with class 5 tiles, such stains cannot be removed and the proper surface has been damaged irreversibly.

Cleaning agents

1) Hot water.

2) Weak commercial cleaning agent.

3) Strong commercial cleaning agent.

4) Solvents (hydrochloric acid, potassium hydroxide, acetone, others to be specified)

Cleaning procedures

A) Running hot water.

B) Manual cleaning with weak commercial cleaning agent.

C) Mechanical cleaning with strong commercial cleaning agent.

D) Immersion in suitable solvent (hydrochloric acid, potassium hydroxide, acetone, others to be specified).

Class 1 - the stain is removed using hot water

Class 2 - the stain is removed using a weak commercial cleaning agent

Class 3 - the stain is removed using a strong commercial cleaning agent

Class 4 - the stain is removed using solvent, such as acetone for example

Class 5 - such stains cannot be removed and the proper surface has been damaged irreversibly.

Chemical Admixtures for Concrete

Chemical admixtures are used to improve workability and quality of concrete during mixing, transporting, application, placement, curing and setting time. 

Chemical admixtures are the admixtures that are added to concrete in a very small amount for a specific function to concrete. If chemical admixtures are added more than the defined than it has a very wide range of negative effects on the properties of fresh as well as hardened concrete. 

chemical admixtures are the extra ingredients other than water, cement, and aggregates. These are added to the concrete batch plant during batch mixing or at the start when other quantities are added. Admixtures offer very favorable effects to the properties of fresh or hardened concrete only if proper use of admixtures is made possible.

ASTM C494 specifies the requirements for chemical admixture types.

Type A: Water-reducing admixtures
Type B: Retarding admixtures
Type C: Accelerating admixtures
Type D: Water-reducing and retarding  admixtures
Type E: Water-reducing and accelerating admixtures
Type F: Water-reducing, high range admixtures
Type G: Water-reducing, high range, and retarding admixtures
Type S: Specific performance (  corrosion inhibitors, shrinkage control, alkali-silica reactivity inhibitors, and coloring ) admixtures.

The materials used in the concrete mixtures shall include Type I or Type II cement, pozzolan, fine and coarse aggregates, and air-entraining admixture.
Types F and G admixtures may exhibit much higher water reduction in concrete mixtures having higher cement factors.
Mixtures having a high range water reduction generally display a higher rate of slump loss.
Admixtures that contain relatively large amounts of chloride may accelerate corrosion of prestressing steel.

Nanotechnology

Nanotechnology deals with the fact that properties of materials can change drastically when the size falls below approximately 100 nanometers ( 1 nanometers = 0.000000001 meter ) in at least one dimension. Nano materials have already found applications in several areas in industry and they are also very promising for construction industry. Nano sized particles can be produced in a "top-down" process from larger particles or in a "bottom-up" process from smaller particles.

Nanoparticles are characterized by their chemical composition, size, shape, structure, surface chemistry. And it should be noted, that different methods of synthesis can lead to marked differences in the structure and properties of the nanoparticles.

Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances can become transparent (copper); stable materials can turn combustible (aluminium); insoluble materials may become soluble (gold). 

Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced. In its original sense, anotechnology refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products. One nanometer (nm) is one billionth, or 10⁻⁹, of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12–0.15 nm. By convention, nanotechnology is taken as the scale range 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. The lower limit is set by the size of atoms (hydrogen has the smallest atoms, which are approximately a quarter of a nm diameter) since nanotechnology must build its devices from atoms and molecules.

High Alumina Cement

High alumina cement is a hydraulic binder based on calcium aluminates, rather than calcium silicates which are the basis of Portland cement. These high alumina cement provide specific properties which are ideally suited to certain applied building products. These include self-levelling, rapid hardening, fast  setting and high  strength mortars.
High Alumina Cement is used in applied products either as a hydraulic binder in its own right or as an accelerator of portland cement depending on the final performance required. Although the setting time is similar to that of portland cement, it offers rapid strength development.
Unlike portland cement, high alumina cement does not release free lime during hydration. In concretes with a low porosity, this property gives a good chemical resistance and eliminates the major cause of efflorescence.
High alumina cement may be used as a hydraulic cement on its own or in association with other mineral products such as Portland cement, calcium sulphates and filler or organics such as polymers in liquid or redispersible powder.
The main active constituent of calcium aluminate cements is monocalcium aluminate (CaAl₂O₄, CaO · Al₂O₃, or CA in the cement chemist notation). It usually contains other calcium aluminates as well as a number of less reactive phases deriving from impurities in the raw materials. Rather a wide range of compositions is encountered, depending on the application and the purity of aluminium source used.

Ordinary Portland Cement (OPC)

Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which then chemically combines with the other materials that have been included in the mix to form calcium silicates and other cementitious compounds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'ordinary Portland cement', the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white.

When water is mixed with Portland cement, the product sets in a few hours, and hardens over a period of weeks. These processes can vary widely, depending upon the mix used and the conditions of curing of the product, but a typical concrete sets in about 6 hours and develops a compressive strength of 8 MPa in 24 hours. The strength rises to 15 MPa at 3 days, 23 MPa at 1 week, 35 MPa at 4 weeks, and 41 MPa at 3 months. In principle, the strength continues to rise slowly as long as water is available for continued hydration, but concrete is usually allowed to dry out after a few weeks and this causes strength growth to stop.

White Portland cement or white ordinary Portland cement (WOPC) is similar to ordinary, grey, Portland cement in all respects, except for its high degree of whiteness. Obtaining this colour requires high purity raw materials (low Fe₂O₃ content), and some modification to the method of manufacture, a.o. a higher kiln temperature required to sinter the clinker in the absence of ferric oxides acting as a flux in normal clinker. As Fe₂O₃ contributes to decrease the melting point of the clinker (normally 1450 °C), the white cement requires a higher sintering temperature (around 1600 °C). Because of this, it is somewhat more expensive than the grey product. The main requirement is to have a low iron content which should be less than 0.5 wt.% expressed as Fe₂O₃ for white cement, and less than 0.9 wt.% for off-white cement. It also helps to have the iron oxide as ferrous oxide (FeO) which is obtained via slightly reducing conditions in the kiln, i.e., operating with zero excess oxygen at the kiln exit. This gives the clinker and cement a green tinge. Other metallic oxides such as Cr₂O₃ (green), MnO (pink), TiO₂ (white), etc., in trace content, can also give colour tinges, so for a given project it is best to use cement from a single batch.

Cement as a Binder

A cement is a binder, a substance used for construction that sets, hardens and adheres to other materials, binding them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement is used with fine aggregate to produce mortar for masonry, or with sand and gravel aggregates to produce concrete.

Cement starts to set when mixed with water which causes a series of hydration chemical reactions. The constituents slowly hydrate and the mineral hydrates solidify; the interlocking of the hydrates gives cement its strength. Contrary to popular perceptions, hydraulic cements do not set by drying out; proper curing requires maintaining the appropriate moisture content during the curing process. If hydraulic cements dry out during curing, the resulting product can be significantly weakened.

Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as being either hydraulic or non-hydraulic, depending upon the ability of the cement to set in the presence of water.

Non-hydraulic cement will not set in wet conditions or underwater; rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.

Hydraulic cements (e.g., Portland cement) set and become adhesive due to a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet condition or underwater and further protects the hardened material from chemical attack. The chemical process for hydraulic cement found by ancient Romans used volcanic ash (pozzolana) with added lime (calcium oxide).

Structural Engineering

Structural engineering involves the analysis and design of the built environment (buildings, bridges, equipment supports, towers and walls). Those concentrating on buildings are sometimes informally referred to as "building engineers". Structural engineers require expertise in strength of materials, structural analysis, and in predicting structural load such as from weight of the building, occupants and contents, and extreme events such as wind, rain, ice, and seismic design of structures which is referred to as earthquake engineering. Architectural Engineers sometimes incorporate structural as one aspect of their designs; the structural discipline when practiced as a specialty works closely with architects and other engineering specialists.

Structural engineering is concerned with the structural design and structural analysis of buildings, bridges, towers, flyovers (overpasses), tunnels, off shore structures like oil and gas fields in the sea, aerostructure and other structures. This involves identifying the loads which act upon a structure and the forces and stresses which arise within that structure due to those loads, and then designing the structure to successfully support and resist those loads. The loads can be self weight of the structures, other dead load, live loads, moving (wheel) load, wind load, earthquake load, load from temperature change etc. The structural engineer must design structures to be safe for their users and to successfully fulfill the function they are designed for (to be serviceable). Due to the nature of some loading conditions, sub-disciplines within structural engineering have emerged, including wind engineering and earthquake engineering.

Materials Engineering

Materials science is closely related to civil engineering. It studies fundamental characteristics of materials, and deals with ceramics such as concrete and mix asphalt concrete, strong metals such as aluminum and steel, and thermosetting polymers including polymethylmethacrylate (PMMA) and carbon fibers. Materials engineering involves protection and prevention (paints and finishes).

Alloying combines two types of metals to produce another metal with desired properties. It incorporates elements of applied physics and chemistry. With recent media attention on nanoscience and nanotechnology, materials engineering has been at the forefront of academic research.

Civil Engineering

Civil engineering is the application of physical and scientific principles for solving the problem.  It is linked to advances in understanding of physics and mathematics. Civil engineering is a wide-ranging profession, including several specialized sub-disciplines, it is linked to knowledge of structures, materials science, geography,  geology, soils, hydrology, environment, mechanics and other fields. 

Civil engineers apply the principles of geotechnical engineering, structural engineering, environmental engineering, transportation engineering and construction engineering to residential, commercial, industrial and public works projects of all sizes and levels of construction. Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings.

Civil engineering takes place in the public sector from municipal through to national governments, and in the private sector from individual homeowners through to international companies.