STRENGTH ASSESSMENT OF CONCRETE SUBJECTED TO ALKALINE MEDIA

Abstract

The aim of any structural design is to achieve an acceptable probability that structures being designed will perform satisfactorily during their intended life with an appropriate degree of safety. They should sustain all loads and deformation of normal construction and use, and have adequate durability and resistance to the effect of misuse.

The durability of concrete can be defined as its resistance to deterioration resulting from external and internal causes. The external causes include the effects of environmental and service conditions to which concrete is subjected, such as weathering, chemical actions and wear. The internal causes are the effect of interaction between the constituent materials such as alkali aggregate reaction, volume change, absorption and permeability.

This research work is to assess the structural strength of concrete cubes cured in varying concentration of a number of alkali solutions. Two grades of concrete, 30 and 40 were used. The concrete cubes were cured in aqueous solutions of Sodium hydroxide (NaOH), Potassium hydroxide (KOH) and Calcium hydroxide (Ca(OH)₂) of 20, 40, 60 and 80 percent concentrations. Compressive strength test was conducted on the cubes at the end of 7, 14 and 28 days immersion period.

The compressive strength of concrete cubes immersed in water (control cubes) increased steadily from 30.96 N/mm² to 35.26 N/mm² at the end of 28 days of immersion for grade 30 concrete and from 40.07 N/mm² to 42.52 N/mm² at the end of 28 days of immersion for grade 40 concrete Generally, the compressive strength increased steadily for cubes in 0 percent concentration of alkali solution up to 40 percent concentration of alkali solution beyond which it started falling, irrespective of the immersion periods for the two grades of concrete.

The influence of alkaline media on concrete is such that the higher the grade of concrete, the more aggressive is the attack on the concrete.