Concrete is considered globally as one of the oldest man-made construction material used for various structures such as bridges, dams, tunnels, buildings, sewerage systems, pavements, runways, roads and fertilizer plant. It has been in existence in varying form for thousands of years and is the second most consumed substance in the world after water (The Cement Sustainability Initiative, 2009). Concrete is made by mixing water, cement, coarse aggregate, fine aggregates and sometimes special admixtures in required proportions. Cement is the primary constitute of concrete, is produced and used in large quantities. In Malaysia, the cement production was 1846 thousands of tonnes in April, 2016 (Trading Economics, 2016). Aggregates of both fine and coarse are commonly considered as filler and they make the body of the concrete structure. Typically, in a concrete, cement occupy about 10 to 15% volume, aggregates about 60 to 70% and water about 15 to 20%. Sometime, entrained air bubbles in concrete mixtures may also take up another 5 to 8 percent (PCA, 2016). Macroscopically, concrete consist of two phases namely, (i) mortar phase and (ii) coarse aggregate phase. The coarse aggregate phase is generally stronger than the mortar phase and is responsible for the unit weight, dimensional stability and elastic modulus of the concrete Tarun (1997).
The mortar phases are interconnected from one end to other while the coarse aggregate phase is disconnected. Mortar phase in concrete plays