Concreting with Chloride Contaminated Aggregates: Effect on Compressive Strength and Concrete – Rebar Bond Strength

Abstract

This study investigates the effect of chloride contaminated aggregate

on the compressive and concrete rebar-bond strength of concrete.

The coarse aggregates were contaminated by immersing them in a

sodium chloride (NaCl) solution for a specified period of time. Two

NaCl solutions were used - 10mg/L and 40mg/L. The aggregates

were contaminated by soaking them in the NaCl solutions for 7 days,

and thereafter left to dry under air for 3 days. Three concrete mixes

were utilized for the study – C0, C10 and C40. C10 and C40 mixes

were prepared with coarse aggregates contaminated with NaCl

solutions of 10mg/L and 40mg/L respectively; while the C0 mix,

which was the control mix, was prepared with uncontaminated

coarse aggregates. A mix ratio of 1:1.5:3.53 was employed, to

prepare concrete cubes which were cured under water for various

periods up to 56 days. Compressive strength and pull-out tests were

carried out on the cured concrete samples. The results revealed that

the concrete mixes containing chloride contaminated aggregates had

higher early strengths (at 3 and 7 days) than the control mix.

However, at later ages of 28 days and beyond, the trend reversed

with the compressive strength of the control mix becoming greater

than that of the concrete mixes containing chloride contaminated

aggregates. The results of the pull-out test showed a decline in the

rebar-bond strength as the concentration of the NaCl solution used

in contaminating the coarse aggregates increased. This study

therefore shows that the effect of the use of chloride contaminated

aggregates on the compressive strength of concrete worsens with the

concrete age and reduces the concrete-rebar bond strength, and thus

should be avoided at all cost.