Effect of fine sand of Hong river on properties of fresh and hardened concrete

Abstract

For many years, fine sands from deposits along several rivers in Vietnam were not effectively exploited for manufacturing of building materials, especially for concrete products. It is caused by limitation in standard specification and lack of strong technical support. This study aims to expand application of the river's fine sand in producing ready mix concrete. In this research, we investigate the effect of the Hong river's and the Lo river's sands with fineness modulus from 1.0 to 2.5. Experimental results show that when fineness modulus of sand decreases, both water demand and segregation of fresh concrete are increased. The increments can be cut down by increasing water-reducing admixture dosage and using an adequate compaction regime. Decreasing maximum coarse aggregate size from 40 mm to 10 mm also reduces segregation. Variation of mortar excessive coefficient from 1.25 to 1.76 has limited effect on compressive strength. Meanwhile, increasing the sand to aggregate ratio dramatically reduces slump of fresh concrete, especially when fine sands were used. Fitting equations between cement to water ratio and compressive strength were studied. The results show that the cement to water ratio of concrete using finer sand needs to be increased to maintain compressive strength.