Admixtures

ACI defines HRWR as a water-reducing admixture capable of producing large water reduction or great flowability without causing undue set retardation or entrainment of air in mortar or concrete. ASTM set the limit for water reduction of HRWR at a min of 12%. Neither ASTM nor ACI define MRWR. These products have been developed out of an industry need. Most all of them pass ASTM C494 Type A – Water Reducing Admixture Standards. Some of the even pass the requirements for HRWR. The main difference is the overall water reduction that can be reached at the higher end of the dosage range. Most MRWR would also start to have some excessive retardation once dosages go higher. Another key point is that some formulations of MRWR have a workability enhancer added, which can results in better finishability. All-in-all however, the application and the water reduction determines whether the product is considered a MRWR. In many applications that are typically more suited for MRWR, HRWRs have been used very successfully.