Studies on Compatibility between Slipform Paving Cement Concrete and Complex Admixtures

The slipform paving technique has been utilized widely in the construction of high-class highway cement concrete pavements in China, resulting in increased use of complex admixtures. Complex admixtures usually contain various components that may have potential compatibility issues, not only between admixtures and cement, but also between admixture components. In order to alleviate or eliminate potential incompatibility problems, it is necessary to adjust the mix proportions and admixture chemical components by taking into account the real-life materials and surrounding conditions. An optimum dosage of the complex admixture should be determined according to the specific job requirements and construction technique. Compatibility issues always arise between admixtures and cements. It was found that ${\mathrm{Na}}_2\mathrm{S}{\mathrm{O}}_4$ and $\mathrm{Ca}{\mathrm{Cl}}_2$ may increase the early strength, but also may reduce the slump of the mix. When the resin-based air-entraining agent and water reducers were used together, they produced a large amount of residue. Water-retaining polymer can be used as the plasticizing ingredient to slow down hardening without sacrificing slump loss and setting time. It is necessary to reduce the ${\mathrm{C}}_3\mathrm{A}$ content so as to enhance the compatibility between retarders and cements. Retarding admixtures based on lignosulphonic or hydroxylated carboxylic acids can delay the setting of cement paste, but also may accelerate the setting when the dosage is high. Blended cements require much more air-entraining agent than Portland cements. The air content decreases as the alkalinity and fineness of cement increase.