Autogenous shrinkage reduction and strength improvement of ultra-high-strength concrete using belite-rich Portland cement

Abstract

Autogenous shrinkage is a non-trivial problem affecting the use of ultra-high-strength concrete (UHSC). Hydration is an important cause of autogenous shrinkage. This study proposes a method to reduce autogenous shrinkage and increase strength by controlling the hydration reaction of the binder. Belite-rich Portland cement (BPC) was used to replace a fraction of the type I ordinary Portland cement (OPC) in the binder (replacement ratios of 33%, 66%, and 100%), and the hydration heat, autogenous shrinkage, compressive strength, hydration products, ultrasonic pulse velocity, electrical resistivity, and CO2 emissions were simultaneously determined. The results are summarized as follows: 1) With increasing BPC substitution ratio, the autogenous shrinkage of the specimen decreased because the addition of BPC lowered the hydration rate. 2) The addition of BPC reduced the early compressive strength (3 and 7 d) and promoted the development of long-term compressive strength (28 and 56 d). 3) The microstructural analysis showed that compared with the control group, the low reactivity of BPC leads to less Ca(OH)2, AFt, and AFm production. 4) The ultrasonic pulse velocity and strength had a strong linear relationship for various specimens at different ages. 5) The electrical resistivity gradually decreased as the amount of BPC substitution increased. 6) The addition of BPC reduced the normalized CO2 emissions per MPa of strength. In summary, upon replacing OPC with BPC, UHSC exhibited lower autogenous shrinkage, lower cumulative hydration heat, lower CO2 emissions, and higher long-term strength.