Of interest to specifying engineers and architects is the new ACI 212.3R-10Report on Chemical Admixtures for Concrete. This official guide has a substantially clarified the confusion specifies face in the choice of waterproofing admixtures to specify for projects especially in areas susceptible to Hydrostatic conditions ________________________________________________________________________________
This report examines three classes of admixtures that in some way reduce the permeability of concrete. The classes are hydrophobic or water-repellent chemicals, mineral fillers, and crystalline materials. In addition, the report defines two sub-categories for admixtures intended to reduce water ingress as either a PRAN – for concrete not subject to hydrostatic pressure, or as a PRAH – for concrete that is subject to hydrostatic pressure.
This ACI report is particularly timely and important because of the importance of permeability to the durability of concrete. Concrete is porous by nature, factor in the real life challenges of concrete placement on site, and then it becomes clear why the best of concrete specification is still susceptible to water attack. Water corrodes reinforcement, acts as a medium for transporting AAR into the concrete, thereby compromising the integrity of concrete.
It is no wonder why every consultants, architects and Structural Engineers recognize the need to specify waterproofing admixtures for concrete. They challenge however, is that there are so many admixtures in the market, with many confusing claims that specifying an admixtures can some time look like playing a lotto game unless one is a connoisseur of admixture knowledge. Thankfully ACI 212.3 R-10 has solved this problem and simplified the process.
ACI 212R PRAH AND PRAN WATERPROOFING ADMIXTURE CLASSIFICATION
PERMEABILITY REDUCING ADMIXTURES FOR NON HYDROSTATIC CONDITIONS (PRAN)
These types of admixtures are effective in reducing the absorption and ingress of chlorides into concrete but usually only under non-hydrostatic conditions and thus are usually classified by ACI 212 as PRANs. Examples are water repellent or hydrophobic admixtures based mostly on fatty acid derivatives called stearates, others are based on Waxes, oily emulsions,talcs, bentonites,clay etc .
While these materials will often densify the matrix and possibly shrink the pores of the concrete and restrict water passage, they typically do not fully block all pores and will not be effective in area with high hydrostatic pressure and as such are classified as PRANs.
PERMEABILITY REDUCING ADMIXTURES FOR HYDROSTATIC CONDITIONS (PRAH)
ACI 212 defines crystalline based admixtures as hydrophilic materials that reacts with water in concrete to form an insoluble Crystalline structures that seal pores, capillaries and micro cracks.The pore blocking deposits generated by the crystals significantly improves the concrete ability to resist water under hydrostatic conditions. The result is permanently dry concrete that is protected against water attack under pressure both now and in the future.
The ACI 212.3R document recommends PRAH type admixtures for applications that will experience hydrostatic head such as below grade, foundations and water retaining structures. The ACI 212.3R document further recommends that PRAH admixtures must pass permeability tests such as the US Corp of Engineers C48, DIN 1048 or BS EN 12390. It is important that specifiers review the datasheets of admixtures to be sure that such products meets minimum permeability test standard conducted by independent bodies before such admixtures are specified for projects in areas with hydrostatic conditions.
Schomburg Group Aquafin Admix and Betocrete 3rd generation Crystalline admixtures product ranges would be classified as PRAH and have excellent crack healing properties. As such, Aquafin admixtures are ideally suited for concrete that will need to perform in the most severe waterproofing applications. Furthermore, Aquafin -treated concrete improves many of the other engineering properties of concrete such as its performance under hot weather placement, corrosion resistance, chemical resistance and carbonation resistance.
Many of manufacturers of construction chemicals especially from Asia have for years suggested that their active or inert pore blocking technology will give performance similar to Schomburg Aquafin product ranges, but this recently released document from ACI suggests other- wise. The latest copy of the ACI 212-3R-10 is available on-line from ACI International and is suggested reading for Specifiers, consultants, architects and contractors.
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