A novel approach to reduce the shrinkage of cement-based materials: pH-responsive admixture from hydrophilic to hydrophobic transformation

One of the effective ways to reduce the risk of concrete cracking is the reduction of drying shrinkage by adding shrinkage-reducing admixture (SRA), which is generally based on the mechanism of reducing surface tension. According to Young-Laplace equation, the mechanism of increasing contact angle should also be very effective. However, the increase of hydrophobicity of admixture would inevitably lead to the decrease of compatibility and effectiveness, which still has been unsolved. This study aims to provide a novel approach for decreasing capillary pressure to reduce the shrinkage of cement-based materials by designing a new admixture with pH-responsive characteristics, which can spontaneously achieve the hydrophilic to hydrophobic transformation through the alkaline environment of cement pore solution. Excellent pH-response and shrinkage reduction in cement mortars were shown. Most importantly, this novel approach was proved to be effective, which had great potential in inhibiting the shrinkage and cracking of cement-based materials.