Drying shrinkage of fibre-reinforced lightweight aggregate concrete containing fly ash

Abstract

Lightweight aggregate concretes containing fly ash with a compressive strength between 61 to 67 MPa were produced. The lightweight aggregate used was sintered fly ash. The concretes were reinforced with either polypropylene or steel fibres. The fibres did not affect the compressive strength, but did increase the tensile strength of these concretes. The modulus of elasticity of all the lightweight concretes tested was about 21 GPa, compared to 35 GPa for the normal-weight concrete. Fibre reinforcement did not affect the value of the elastic modulus. This type of lightweight concrete, containing fly ash as 23% of the total cementitious content, resulted in long-term shrinkage that is nearly twice as large as normal-weight concrete of somewhat similar strength. Polypropylene fibre reinforcement did not reduce drying shrinkage, while steel fibres did. Early shrinkage behaviour of this type of lightweight concrete was similar to normal-weight concrete. However, the rate of shrinkage of the lightweight concrete remained constant until nearly 100 days of drying. This is different from normal-weight concrete that slowed appreciably after 56 days. Shrinkage of normal-weight concrete stabilised after 400 days, while shrinkage of lightweight concrete did not appear to stabilise after a similar period of continuous drying.