Increasing Pile and Anchor Capacity in Rock by using Expansive Cement Additives

The use of an expansive cement admixture to increase pile and anchor capacities in rock is discussed. The admixture promotes internal sulphate attack of the concrete forming the pile, which, in turn, result in the concrete expanding against the surrounding rock. If the rock is capable of withstanding this expansion, then substantial stresses normal to the concrete-rock interface can be developed. The fundamental model of friction prescribes that if the stresses across the concrete/rock interface are increased, then the frictional resistance of the interface should also rise, thereby resulting in an increase in pile and anchor capacity. The results of laboratory investigations into the determination of the likely increases in pile capacity are described.