The Mechanism of Expansion Stress Produced by Hydration of Compacted CaSO4•2H2O-C3A

The expansive stress produced by compacted CaSO4•2H2O-C3A soaked in water, Ca(OH)2-saturated solution and 1 mol/L NaOH solution was measured by a self-designed device, and the swelling expansive stress of the ettringite hydrated by CaSO4•2H2O-C3A compact.The results show thatettringite was the only product in compacts immersed in water and solutions. The maximum expansive stress produced by the compacts cured in 40℃ water, Ca(OH)2-saturated solution and 1 mol/L NaOH solution was 23.9 MPa, 27.3 MPa and 26.4 MPa, respectively. Lower expansive stress of the compact hydrated in water than that hydrated in Ca(OH)2-saturated solution and 1mol/L NaOH solution seems to indicate that both Ca(OH)2-saturated and NaOH solution may promote the expansive stress of ettringite formation. However, the maximum expansion stresses due to the swelling of the generated ettringitein compacts cured in 40℃ water, 1 mol/L NaOH solution and Ca(OH)2-satura-ted solution only were about 1.23 MPa, 1.27 MPa and 1.26 MPa, respectively. The swelling pressure is much lower than the expansive stress generated by hydration of CaSO4•2H2O-C3A compacts. This indicates that crystallization pressure of the ettringitewas the main reason of expansion stress and the swelling stress of ettringite had little contribution. © 2019, Materials Review Magazine. All right reserved.