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Concrete is by far, the most widely used construction material in the world today. But the use of concrete does not come without certain associated and inherent problems, such as shrinkage cracks. Concrete will normally crack, and this phenomenon is what CONEX is about. There are many different kinds or types of cracks that are associated with concrete, and CONEX is not the answer to all of them. Cracks caused by settlement and other types of structural cracks, or cracking that occurs while the concrete is in a plastic state (plastic shrinkage) cannot be eliminated by including CONEX in the mix. CONEX has over 20 years of field usage with the goal to minimize or eliminate cracking that is caused by drying shrinkage. In concrete it takes relatively little water to completely hydrate the cement, in a typical mix approximately 21 pounds of water per 100 pounds of cementitious materials used. Any additional water is strictly “water of convenience”, which means it is included solely to make the mix more workable. After the mix sets, and during hardening, this water of convenience begins to evaporate, causing the concrete to shrink. If the concrete is completely unrestrained, this shrinkage will occur very slowly and may not be noticed, but concrete can never be completely unrestrained. Restraint comes from the base upon which the concrete is placed, bonding to structures that are already in place (such as walls, columns, etc.), and from the reinforcing steel that is designed into the structure itself. This restraint creates tensile stresses in the concrete, and when these stresses become greater than the tensile strength of the concrete, the result is cracking. This is the reason that control joints are used in concrete. With CONEX the use of control joints can be decreased substantially. When CONEX is used in the mix, there is an initial expansion due to the formation of calcium hydroxide platelets, which in turn bond to the reinforcing steel. This expansion creates a concrete which instead of succumbing to tensile stress (and subsequent cracking), is placed into compression. After curing, as the concrete is allowed to dry, because of the internal expansive strains placed upon the concrete through the action of CONEX, the tendency for cracking due to drying shrinkage is greatly minimized or eliminated. As expressed in ACI-223, “ideally, a residual expansion will remain in the concrete, thereby eliminating shrinkage cracking”. This type of residual expansion can be achieved with CONEX, and will depend on the dosage of CONEX as to how much restrained expansion (RE) residual is left after long term drying. CONEX is not a shrinkage-reducing admixture (SRA), but rather a shrinkage compensating component that, if desired, may be used at a lower dosage rate (approximately 3%-4%) to achieve a minimum shrinkage level that may be required on specifications calling for an SRA. CONEX can be used with 99+% of the cements produced today, to form a shrinkage-compensating concrete with minimum to maximum shrinkage correction (compensation) or elimination. CONEX will expand initially (within 24-48 hours depending upon the type of cement in use), with the formation of calcium hydroxide platelets, creating a unique and necessary expansion in the concrete that will compensate for the drying shrinkage that occurs. | What is CONEX | Chemistry | Concrete Characteristics | Facts about SCC | CONEX & Floor Slabs | Pre-Stressed | Links | | Return Home | CONEX | Projects | What's New | Our Services | Contact Us | |
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