Spring 2007

 

 Properties of Concrete Made with Different Aggregates

Md. Minhaz Rahman and Dhali Md. Al-Azad

 

A detailed study on the properties of concrete made with commonly used aggregates in Bangladesh was carried out. The investigated factors were: (1) types of aggregate (brick aggregate, stone chips, shingle, jhama brick chip), (2) surface moisture variation of the brick aggregate, (3) dust contaminated sand, and (4) pre-heated and cement-paste coated aggregates. The aggregates were investigated for absorption capacity, unit weight, FM, abrasion, etc. Concrete cylinders of size 15 cm in diameter and 30 cm in length were made. Concrete was investigated for workability, unit weight, stress-strain curve, compressive strength and Young’s modulus. The strength of concrete was also evaluated by NDT (Non Destructive Test) before testing by UTM (Universal Testing Machine). A Schmidt hammer was used for NDT. The following conclusions were made:

 

Types of Aggregate

For W/C =0.55, concrete made with brick chips shows the highest compressive strength than other coarse aggregate. Concrete made with aggregate of a higher abrasion value shows higher strength. This observation is very clear for less W/C. Similar results were found for Young’s modulus of concrete.

 

Surface Moisture Variation of the Brick Aggregate

At 28-day, no significant variation of compressive strength of concrete is found for concrete made with Saturated Surface Dry (SSD) aggregate, Air Dry (AD) aggregate, Control Air Dry (CAD) aggregate & Oven Dry (OD) (OD) aggregate. But in case of concrete made with aggregate with Surface Water (SW) gives significantly less strength. 

 

Dust Contaminated Sand

Normal concrete shows higher compressive strength compared to dust contaminated sand. Sand with the dust passing through #200 sieve (maximum 10%) gives the highest compressive strength of mortar compared to the other cases investigated here. The case with dust contaminated sand (#100 sieve passing and #200 sieve retained) shows significant improvement of workability of concrete. More investigations are necessary on this matter.

 

Pre-Heated and Cement-Paste Coated Brick Aggregates

To improve the ITZ of brick aggregate, investigations with cement paste coated (W/C=0.5 for cement paste coating) brick aggregates, & pre-heated (40⁰c) brick aggregates were carried out. W/C of concrete was 0.55. The compressive strength & Young’s modulus of concrete was evaluated at 7, 14, 28 days. Cement paste coating over the brick aggregate as well as pre-heated brick aggregates improves the compressive strength & Young’s modulus by 10-15% compared to the same made with normal brick aggregate.