Comparing Effects on Portland Cement Mortar Containing Micronized Rubber Powder (MRP) and Fine Ground Waste Tire Rubber Intended for Freeze-Thaw Durability

Research into using crumb rubber from waste tires in asphalt pavements has been extensively studied; however, crumb rubber use in concrete has been conducted with results that are varied and conflicting in many cases.This study attempted to determine if the type of crumb rubber is relevant to its inclusion in cement mortar. For example, producers of cryogenically processed micronized rubber powder (MRP) has seen restrictions to its use in rubber modified asphalt binder; based on requiring increased particle surface area. The consensus of crumb rubber’s interfacial bond strength with cement paste is that it is minuscule compared the bond with natural ridged aggregates. If crumb rubber is considered as a non-bonding aggregate, then the surface area argument is not relevant to inhibit a type of crumb rubber from being used in cement concrete applications.The results of compressive strength, modulus of rupture, and splitting tensile resistance showed no statistical difference in mechanical properties when using either cryogenically or non-cryogenically processed crumb rubber. The results of rapid chloride-ion penetration (RCP), freezing-and-thawing durability (FT) and bulk water absorption showed no significant difference when using either type of crumb. The difference in RCP in rubberized mortar and non-rubberized mortar was directly correlated with the volumetric difference of cement paste content. Rubberized mortar’s freeze-and-thawing durability was analogous to non-rubberized high-strength mortar having five times the compressive strength.The only properties greatly affected by the type of crumb rubber were density and workability of fresh cement mortar. The MRP rubber product had no detrimental effects to mortar flow and may prove to increase the effect of a polycarboxylate based water-reducer on workability. Non-cryogenically processed waste tire rubber showed to negate any effect to percent flow provided by a water-reducer.