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We know the more you learn about concrete, the better informed decisions you will be able to make for your home, business, or community. Below are resources for you to learn more about concrete and why it is the most versatile, affordable, and green material for your construction needs.



Basics of Concrete - Concrete Glossary

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Absorbed Moisture - The moisture within the pores and capillaries of an aggregate.

Absorption - The process by which a liquid is drawn into the pores of a porous solid body; also, the increase in mass of a porous solid body resulting from the penetration of a liquid into its permeable pores.

ACI - American Concrete Institute

Accelerators - An admixture that causes an increase in the rate of hydration of hydraulic cement, and thus shortens the time of setting, or increases the rate of strength development, or both. Accelerators come in chloride and non-chloride versions. It should be cautioned that these materials are not anti-freeze agents.

Admixture - Any material that is added to a batch of concrete other than water, aggregate, cement and fiber reinforcement. This includes materials introduced before and during the mixing process. These materials are subdivided into two categories, being, chemical and mineral.

Aggregate - Materials such as sand and crushed stone, which make up about 60% to 80% of concrete's volume. These are considered inert fillers.

Air Content - The volume of air voids in cement paste, mortar, or concrete, exclusive of pore space in aggregate particles. This measure is expressed as a percentage of total volume of the paste, mortar, or concrete.

Air Dry- A condition of an aggregate at which the particle is dry on the surface but may contain moisture within the pores of the aggregate.

Air Void - An air filled space in cement paste, mortar, or concrete. These voids may be in the form of entrapped or entrained air.

Alkalies - Sodium and potassium that occur in portland cement, either as solid solutions in the cement compounds, or as water-soluble compounds, such as sulfates.

ANSI- American National Standards Institute

ASQ - American Society for Quality

ASTM - American Society for Testing and Materials
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Bag of Cement - One bag of cement always weighs 94 lbs.

Batch - The process of measuring the constituents of concrete as directed by a mix design, and loading these materials in preparation for mixing and the completion of that mixing cycle.

Binder - Hardened cement paste.

Bleed Water - The water that accumulates on the surface of plastic concrete. This is the excess mixing water, which has been pushed out as a result of the consolidation and settlement of freshly placed concrete.

Blended Cement - A product consisting of a mixture of portland cement and other material such as granulated blast-furnace slag, pozzolan, etc., combined either during the finish grinding of the cement or by blending the material after grinding.

Blister - A raised spot on concrete, which will often pop off. It is caused by air and/or bleed water being sealed under the surface of a slab.

Broom Finish - A slip-resistant surface created by brooming the top of the concrete before it has thoroughly hardened.

Bulk Density - The mass of a unit volume of bulk aggregate material. This unit volume includes the volume of the individual particles as well as the volume of the voids between the particles. This term replaces the term "unit weight".
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Calcination - Decomposition due to the loss of bound water and carbon dioxide.

Calcium Chloride - A crystalline product that may be sold in liquid, flake, or pelletized form. Some of its many uses are as an accelerator in concrete, as a drying agent, and as a de-icer.

Cellular Concrete - A lightweight concrete that has a porous cell structure which is obtained through the use of foaming agents or gas-forming chemicals.

Cement - Clinker interground with gypsum. This is the binder in concrete.

Cement Factor - This is the number of pounds or bags of cement in one cubic yard of concrete.

Cement, Type I - A general-purpose cement.

Cement, Type II - Used where moderate sulfate attack is likely. Type II is also used when a moderate heat of hydration is required. This type serves as a general purpose cement and is often blended with Type I, producing a Type I/II.

Cement, Type III - This cement is used when high early strength gain is required. Type III has a faster rate of hydration resulting in a faster rate of strength gain.

Cement, Type IV - The special property of this cement is a very low heat of hydration. An example of its use would be in a dam, where thermal cracking is very likely, due to concrete being placed in mass.

Cement, Type V - This cement is used when high sulfate resistance is required.

Cementitious - Having cementing properties.

Cementitious (Hydraulic) Material - An inorganic material or a mixture of inorganic materials that sets and develops strength by chemical reaction with water by formation of hydrates and is capable of doing so under water.

Central Mix Plant - The plant operator batches the ingredients and then charges them into a stationary mixer, which then dispenses the fully mixed concrete into the delivery vehicle. Other names for this type of plant are; pre-mix, wet, and shrink mixed plant.

Chemical Admixture - A nonpozzolanic admixture in the form of a liquid, suspension, or water-soluble solid.

Chord Length - The measurement of the size of a bubble.

Clay - Type of soil consisting of very fine particles.

Clinker - The partially fused product that is removed from the cement kiln after burning.

Clinkering - The combination of limestone and clay in a cement kiln which involves the melting of part of the kiln charge.

Coarse Aggregate - Term used to refer to particles typically 3/8" or larger. Generally this refers to stone.

Color Hardener - A method of coloring concrete whereby a colored powder is cast onto the concrete surface while the concrete is still in a plastic state. This material also hardens the top of the concrete by making the surface more dense.

Compression - Forces inwardly acting on a body.

Compressive Strength - The strength of concrete as determined by how much force is required to crush it. This is expressed in pounds per square inch.

Concrete - The world's greatest and most versatile building material. It consist of cement, water, and aggregate. Often its properties are enhanced through the addition of admixtures.

Consistency - A condition of plastic concrete that relates to its cohesion, flow, or wetness. Consistency is measured by a slump test.

Construction Joint - These provide stopping place in the process of construction, where new concrete may be poured right up to existing concrete.

Contraction Joints - Also known as control joints, these joints provide for horizontal movement in the plane of a slab or wall. They induce cracking of the concrete that will happen as a result of drying shrinkage.

Control Chart - A graphical method for evaluating whether a process is or is not in a "state of statistical control".

Controlled Low Strength Material (CLSM) - An engineering term for Flowable Fill. ACI 229R-94 defines CLSM as a self compacted, cementitious material used primarily as a backfill material in lieu of compacted-soil backfill.

Core - A destructive test of hardened concrete where representative samples are cored out of the concrete in-place. These cores are then either tested by petrographic analysis or destroyed by compression testing. Cores usually break lower than cylinders, which were cast and cured properly.

COD Order - A "cash on delivery" order. Unicon Concrete has a pre-pay policy for these incidences.

Crazing - A concrete surface phenomena which has the appearance of spider webs or a road map. It is purely an aesthetic problem. Some causes could be; wetting the surface during finishing, over finishing, or the top could have simply dried out too rapidly while the body was still moist.

Crushed Gravel - The product resulting from the artificial crushing of gravel with substantially all fragments having at least one face resulting from fracture.

Crushed Stone - The product resulting from the artificial crushing of rocks, boulders, or large cobblestones, substantially all faces of which have resulted from the crushing operation.

Cubic Meter - The metric standard of measurement in which concrete is batched, delivered, and sold. One cubic meter equals approximately 1-1/3 cubic yards or about 36 cubic feet.

Cubic Yard - A standard of English measurement in which concrete is batched, delivered, and sold. It equals a volume of 27 cubic feet.

Curing - The process of ensuring that freshly placed concrete is kept in a moist condition while hydrating in order to promote the maximum strength development.

Curing Compound - A liquid that, when applied as a coating to the surface of newly-placed concrete, forms a membrane that retards the evaporation of water to promote curing. These compounds may be either water or solvent based.

Curling - A concrete problem where the slab edges tend to curl upward when the surface of the slab is drier or cooler than the bottom.
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D-Cracking - A series of cracks in concrete near to and roughly parallel to features such as edges, joints, and structural cracks.

Damp Condition - An aggregate that has excess moisture on its surface to the point that it contributes water to the mix.

Deformation - The process of changing the dimensions of a structure by applying force.

Deleterious Substances in Aggregates - Simply put, undesirable substances that may be found in aggregates. Some examples of these substances are: organic impurities, coal lignite, clay silt, and soft particles.

Density - Mass per unit volume.

Dormancy Period - Time period that concrete retains its workability.

Drum - The revolving housing on a mixer truck where the fresh concrete is deposited after it has been batched. The drum mixes the concrete to its proper consistency before leaving the plant and keeps the material mixed while in transit to the job.

Dry Batch Plant - Here the batches are measured and drawn up by the plant operator and charged into the ready-mix truck for mixing.

Durability - The ability of hardened concrete to resist the deterioration caused by weathering, abrasions, and chemicals to which it is exposed.

Dusting - This is the chalking or powdering at the surface of a concrete slab. It indicates that for whatever reason, the wearing surface is weak.
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Elasticity - The ability of a material to return to its original shape after being stretched.

Entrained Air - Microscopic air bubbles intentionally incorporated in mortar or concrete during mixing, usually by use of a surface-active agent, typically between 10 & 100 Ám (1 mm) in diameter and spherical. This provides concrete the ability to resist freeze thaw weathering action.

Entrapped Air - Air voids in concrete that are not purposely entrained. These are the larger bubbles present in the mix which are the product of the agitation involved in the mixing process. The bubble is usually 1 mm or larger in size. Entrapped air serves no real useful purpose.

Expansion Joints - Also known as isolation joints, these joints permit horizontal and vertical movement at adjoining or abutting parts of a structure. Some examples are; around the perimeter of a floor against a basement wall or around columns.

Expansive Cement - A modified portland cement that when mixed with water forms a paste, which increases in volume during the early hardening period o a much greater degree than pastes containing ordinary portland. The three types of expansive cement are; K, M, and S. These are specifically used in shrinkage-compensating concrete.
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False Set - Early stiffening that usually occurs within minutes after mixing portland cement with water. Workability can be restored by further mixing.

Fiber - A synthetic material added to the concrete as an alternative method of secondary reinforcement. The material is usually made of nylon or virgin polypropylene. It also helps reduce shrinkage cracks in early placement of concrete and improves impact resistance.

Final Set - A measure of the time at which paste, mortar, or concrete is able to resist penetration by a standard weighted test needle to a reading of 4000 psi.

Fine Aggregate - Term used to refer to any particle less than 3/8" in size. Generally this refers to sand. This includes both natural sand as well as manufactured sand.

Fineness - A measure of the degree of subdivision of a powder, such as cement. The parameter used is the specific surface area of the particle as determined either by turbidimetry or air permeability measurements.

Fineness Modulus (FM) - A number obtained from the grading of fine aggregate. Sand used in concrete usually has a FM between 2.3 and 3.1. The higher the number, the coarser the sand.

Flash Set - The very rapid stiffening of concrete which can occur when portland cement and water are mixed together, resulting in a high evolvement of heat. Workability cannot be restored without the addition of more water.

Floating - The process done to concrete after it has been placed. Floating entails going over the concrete surface with a float, which is a tool usually made of magnesium or like metal. It smoothes the surface while opening the pores to allow proper bleed water to come to the surface.

Flowresistance - The force required to initiate a movement of concrete.

Flowable Fill - An alternative to compacted soil or stone. See CLSM.

Fly Ash - The finely divided residue that results from the combustion of pulverized coal and is transported from the combustion chamber by exhaust gases. It is a by-product of coal-fired electric generating plants. Fly ash is a pozzolan often used in conjunction with cement to further the strength of concrete. It is considered a mineral admixture.

Form - Since concrete is placed in a "plastic" state, it must be held in place until it hardens. A form is anything used for this purpose and is removed after the concrete has set and hardens.

Free Moisture - The moisture on the surface of an aggregate. Free moisture is calculated as the difference between the total moisture and the absorbed moisture.

Fresh Concrete - Concrete that possesses enough of its original workability so that it can be placed and consolidated by the intended methods.
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Grading - The distribution of particle sizes in aggregates.

Gravel - Coarse aggregate resulting from natural disintegration and abrasion of rock or processing of weakly bound conglomerate.

Grout - A term used in concrete to denote a mix made up of cement, flyash, sand, and water, with the occasional addition of further admixtures. Grouts have many uses such as for priming a pump, for the filling of voids, or may be used as "butter" at the bottom of a formed wall.

Gypsum - Calcium sulfate dihydrate, added to cement to regulate setting.
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Head Water - Water, which is metered into the ready-mix truck at the start of a batch.

Heat of Hydration - The heat liberated when hydraulic cements react with water.

Heavyweight Aggregate - An aggregate of high density; such as barite, magnetite, limonite, ilmenite, iron, or steel.

High-Early Strength Concrete - Specially designed concrete that reaches its strength faster than normal concrete.

High-Range Water Reducer - See definition of Super Plasticizer.

Hydraulic Cement - A cement that sets and hardens by chemical reaction with water and is capable of doing so under water.

Hydration - The chemical reaction between substances and water to form new compounds. In the case of concrete, the reaction is between cement and water.
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Integral Color - Colored pigment that is added to the ready-mix to create colored concrete. Unicon recommends only the use of iron oxide for this purpose, whenever possible, as it is permanent.

Initial Set - An arbitrary measure of the time at which paste, mortar, or concrete can resist to a given degree, the penetration of a standard weighted needle to a reading of 500 psi. This instrument is known as a Pentrometer. In the field, initial set may be considered as the point at which an average weighted adult can stand on the freshly placed concrete without leaving a visible indentation.

ISO Registration - International Organization For Standardization is a Quality Management philosophy utilized globally. We at Unicon Concrete are ISO registered as a validation of our QMS implementation.
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Kiln - High temperature oven.
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Laitance - A layer of weak material derived from cementitious material and aggregate fines either: 1) carried by bleeding to the surface or to internal cavities of freshly placed concrete, or 2) separated from the concrete and deposited on the concrete surface or in internal cavities during placement of concrete under water.

Lightweight Aggregate - An aggregate of low density used to produce lightweight concrete. Some examples include: pumice, expanded clay, shale, or slate, and perlite.

Lightweight Concrete - Concrete which utilizes lightweight aggregate as the coarse aggregate in the mix. It is very similar to normal weight concrete except that it has a lower density. It is mainly used to reduce the dead- load weight in concrete members on elevated floors and for higher fire rating purposes.

Limestone - Mineral rock of calcium carbonate.

Loss On Ignition (LOI) - A test done to cementitious materials whereby a known weight of a sample is heated to between 900 to 1000 degrees Celsius, until a constant weight is obtained. The weight loss of the sample is then determined. Elevated results may indicate carbonation and even prehydration.
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Manufactured Sand - A fine aggregate produced by crushing rock, gravel, iron blast-furnace slag, or hydraulic-cement concrete.

Maturity - The extent of the development of a property of a cementitious mixture. At any age, maturity is dependent on the curing history.

Maximum Size of Aggregate - The smallest sieve opening through which the entire amount of aggregate is required to pass.

Megapascal - Expressed as MPa, it is the metric equivalent to the English measure, psi. One MPa is approximately 145 psi.

Mid-Range Water Reducer - An admixture that will allow concrete to be placed At a looser consistency without impacting strength, while improving finishability and workability. Typical mid-range water reducers reduce water content 8% to 15%.

Mineral Admixture - Generic term for any supplementary cementing material.

Mixer Operator - The Unicon Concrete professional who operates the ready-mix truck and delivers the concrete to our customer, where it is discharged.

Mortar - A mixture of sand, cement, and water.

Mud Mat - A term used to describe a very low strength concrete whose sole purpose is to hold loose soil or embankments in place. It is not structural concrete.
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Non-Chloride Accelerator - A set-enhancing admixture made with no chlorides. It comes into play whenever corrosion of reinforcing materials, such as rebar, are a structural concern, among other uses.

Nominal Maximum Size of Aggregate - The smallest sieve opening through which the entire amount of the aggregate is permitted to pass.
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Oven-Dry - A condition of an aggregate which contains no moisture, either free or absorbed.
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Paste - A mixture of cement and water without aggregates.

Permeability (Concrete) - Concrete permeability is the ability for liquids and gases to pass through the concrete matrix through the interconnecting void spaces inherent to concrete.

Pervious Concrete - A discontinuous mixture of coarse aggregate, hydraulic cement and other cementitious materials, admixtures, and water which allow for the passage of air and water. By capturing stormwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting U.S. Environmental Protection Agency (EPA) stormwater regulations. In fact, the use of pervious concrete is amoung the Best Management Practices (BMPs) recommended by the EPA - and by other agencies and geotechnical engineers across the country - for the management of stormwater runoff on a regional and local basis.

Petrographic Analysis - A test using microscopic techniques to determine the constituents of concrete, concrete quality, and cause of inferior performance, distress, or deterioration.

pH - The measure of hydrogen ion concentration. In water, a value of 7.0 indicates neutrality.

Plastic - The fluid workable state of concrete before it hardens.

Plastic Shrinkage Cracks - Small cracks that sometimes occur in the surface of freshly placed concrete while being finished. This occurs when water evaporates from the surface faster than it can appear at the surface during the bleeding process. This in turn creates rapid drying shrinkage and tensile stresses in the surface that often result in short, irregular cracks.

Pop Out - The breaking away of a small fragment of concrete surface due to internal pressure that leaves a small conical depression.

Porosity - The amount of empty space in concrete.

Portland Cement - The trade name used by Joseph Aspdin in 1824 when he patented his new cement in England. Today the term is still used to denote a material formed by a chemical combination of silica, alumina, calcium carbonate, and iron oxide. Calcium sulfate is usually added in the final grinding process to help regulate setting time.

PSI - Concrete strength is expressed in pounds per square inch.

Pozzolan - A siliceous or siliceous and aluminous material which in itself Possesses little or no cementitious value, but which will in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. An example of this material would be fly ash.

Procedures - The documented practices defining the who, what, and when of quality activities. Singularly, it would be a specified way of doing an activity.
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Quality - The totality of characteristics of an entity that bear on its ability to Satisfy stated and implied needs.

Quality Assurance (QA) - Actions taken by an organization to provide and Document assurance that what is being done and what is being provided Are in accordance with applicable standards of good practice and follow The contract documents for the work.

Quality Control (QC) - Actions taken by an organization producing a product to Provide control and documentation over what is being done and what is being provided so that applicable standard of good practice and the contract documents for the work are followed.

Quality Manual - The document specifying the quality management system of an organization.
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Ready-Mix Concrete - Concrete that has been batched and thoroughly mixed off-site and is delivered to the job-site in a plastic state.

Rebound Test Method - A nondestructive test method where a rebound hammer is used which records the rebound of a spring-loaded plunger after it has struck a smooth concrete surface. This reading gives an indication of the in-place strength of the concrete.

Relative Density - See specific gravity.

Retarder - An admixture used to lengthen the time of set in hydraulic materials.

Rheology - The science of flow and deformation of matter.

Roller-Compacted Concrete (RCC) - Concrete that is compacted while fresh by a roller.
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Sand - Fine aggregate resulting from natural (or machine induced) disintegration and abrasion of rock or processing of completely friable sandstone.

Saturated Surface Dry (SSD) - A condition at which an aggregate will neither absorb moisture from concrete nor contribute moisture to the mix.

Scaling - This is when the surface of concrete flakes or scales off as a result of repeated freeze-thaw cycles.

Screeding - The process of striking off excess concrete to bring the top surface of a slab being placed to proper grade.

Segregation - The unintentional separation of the constituents of concrete or particles of an aggregate, causing a lack of uniformity in their distribution.

Self-Compacting Concrete (SCC) - A special formulation of concrete for use in formed walls, which does not need vibration for placement. Its flowability allows the mix to encapsulate rebar and other reinforcement in the wall. SCC is measured by spread instead of slump.

Setting - Loss of elasticity and formulation of a semi rigid mass of cement paste or concrete.

Silica Fume - A by-product from electric arc furnaces used in the manufacture of silicon metals. It consist of spherical particles which are much finer than fly ash or cement, which is a highly reactive glassy form of silicon dioxide. This material can be used to replace cement in a mix from 5% to 10%. It is used in for special applications where very high strength (in excess of 10,000 psi) concrete is required or low permeability is needed.

Slag - The glassy, granular material that is formed when molten blast-furnace slag is rapidly cooled and blended in a pulverized state with portland cement to form hydraulic mixtures.

Slump - The measure of the consistency and flowability of concrete.

Slump Cone - The instrument used to measure the slump or consistency of concrete. The slump cone was invented in the early 1900's by Abram.

Soundness - The ability of an aggregate to withstand the aggressive actions, to which concrete containing it might be exposed, particularly those due to weather.

Spacing Factor (in Air-Entrained Concrete) - The maximum distance that water would have to move before reaching the air-void system.

Specific Gravity - The ratio between the weight of a material to the weight of an equal volume of water. It is used in the absolute volume computation for concrete mix design and control.

Specification - The document that prescribes the requirements that the product or service has to meet.

Stamped Concrete - A decorative process done to concrete as it hardens where a pattern is stamped or pressed onto the surface. The base concrete is usually colored and a colored release agent is spread upon the top just before stamping. The impression on the surface of the concrete is permanent as long as the concrete remains in place. The end product may look like slate, stone, or brick, just to name a few.

Sulfate Resistance - The ability of a portland cement binder to resist chemical attack by soluble sulfate salts.

Super Plasticizer - A high-range water reducer which greatly reduces the amount of water needed to make concrete flow. This allows ease of placement and consolidation. As the chemical wears off, the concrete reverts to its original consistency with a higher end strength. Typical high-range water reducers reduce water content 12% to 30%.

Supplier - An organization that provides a product to an owner.
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Tail Water - The water discharged into the batch at the tail of the cycle. This is usually anywhere from 15% to 30% of the total batch water.

Tensile Strength - A measure of hardened concrete's ability to withstand tension.

Tension - The stress resulting from elongation.

Thixotropy - As defined by British Standard BS 5618: 1976, thixotropy is a decrease of apparent viscosity under shear stress, followed by gradual recovery when the stress is removed. The effect is time-dependent.

Total Moisture - The sum of the moisture on the surface and the absorbed moisture of an aggregate.

Total Weight of Batch - The sum of the weights of all constituents in a cubic yard of concrete.

Troweling - This process follows floating, after much of the bleed water has evaporated. It is done by applying a steel trowel to the surface, often in the form of a trowel blade on a finishing machine. Troweling is used any time a smooth, hard, dense, surface is required.
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Unit Weight - The weight per unit volume. As it pertains to concrete, the unit weight is expressed as pounds per cubic foot.
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Viscosity Factor - A measure of the resistance of the concrete against an increased speed of movement.
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Water-Cement Ratio - The weight ratio of the amount of free water (not contained in aggregates) to the amount of cement in a paste, mortar, or concrete. In other words, the weight of the water used is divided by the weight of the cement used in the concrete mix design. This ratio is expressed as a decimal fraction. The lower the water-cement ratio, the stronger the concrete.

Water of Convenience - The water beyond the minimum necessary for hydration, which is used to make concrete plastic and workable.

Water of Necessity - The minimum water required in concrete for complete hydration.

Water-Reducer - An admixture for water reduction in concrete. This helps maintain a slump and increase strength by being able to mix the concrete with less water. Typical water-reducers reduce the water content by approximately 5% to 10%.

Water Vapor - Water in a gas state. Water vapor moves faster and much more readily through concrete than water in its liquid state. Therefore, waterproof concrete does not stop water vapor. When water vapor reaches the dew point under flooring materials it condenses becoming water. This often leads to deteriorating the adhesive or the flooring itself attached to the concrete, leading to a failure. This is why a vapor barrier must be used under the slab, when the concrete is to be used in a "living" area.

White Portland Cement - An architectural cement which is white versus the standard gray associated with typical cements. This cement generates more heat than a Type I and has early strength gain characteristics.

Workability - That property of freshly mixed paste, mortar, or concrete which determines the ease with which it can be mixed, placed, compacted, and finished.
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Yield - The actual volume of a cubic yard of concrete. The yield is derived by taking the total weight of the batch and dividing it by the unit weight.
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