Because the induced expansion and shrinkage are generally not synchronous, the effectiveness of a shrinkage- compensating system is dependent on restraint during the expansive process to produce a compressive prestress that will decrease with subsequent shrinkage. In new construction, a minimal amount of reinforcement is used to provide this restraint, as recommended in ACI 223R. There is no such provision for repair materials, and it certainly requires some attention, especially in the case of bonded surface repairs without reinforcement where the restraint is provided by simple interface bond with the substrate and, depending on the confguration of the repair (partial-depth versus overlay work), by abutment to the vertical edges. Information on the dimensional behavior of shrinkage-compensating or nonshrink repair materials is generally insuffcient or absent from the manufacturer’s data sheets. This lack of information is due, in part, to the absence of explicit standardized test procedures and specifcations for shrinkage-compensating materials. ASTM C1107/ C1107M requires that the height change of moist-cured hardened hydraulic-cement grout be within the range of 0 to +0.3 percent when tested in accordance with ASTM C1090/C1090M. In the case of rapid-hardening cementi- tious materials for concrete repairs (ASTM C928/C928M), many of which are also claimed to be shrinkage- compensating, the maximum allowable increase in length change is 0.15 percent after 28 days in water and the maximum allowable decrease is –0.15 percent after 28 days in air. This range for maximum allowable expansion and contraction is so permissive that most materials fall between the limits. Also, there are no requirements for rate of volume change for rapid-hardening cementitious repair materials.
Summary All cementitious materials undergo some drying shrinkage when exposed in an environment where relative humidity is below 100 percent. The labels ‘shrinkage-compensating’ and ‘nonshrink’ found in the technical data sheet of some prepackaged repair materials mean that they are formulated to exhibit no resulting net contrac- tion upon drying, owing to a chemical expansion process taking place in the early stages of curing. Proper selec- tion and use of such repair materials requires the knowledge of adequately referenced test data on the actual time-dependent volume changes the material undergoes during and after curing.ACI 364.15T pdf download.