Sawdust Ash as Powder Material for Self-Compacting Concrete Containing Naphthalene Sulfonate

Tests are carried out to determine the fluidity of Ashaka Portland cement paste and its compatibility with sawdust ash (SDA) as powder material for self-compacting cement (SCC) mixtures. Results of the investigation showed that saturation was achieved at w/c ratios of 0.4 and 0.42, at dosages of naphthalene sulfonate superplasticizers of 3.5% and 2%, respectively. The optimum replacement level for the SCC mixture was 10？wt.% of cement by SDA and 2% of the superplasticizer dosage. The achieved spread and flow time were 26？cm and 8 seconds and are within the specified range of 24？cm to 26？cm and 7 to 11 seconds, respectively. Statistical inference showed that the mix, w/c, and the interaction between the mix and w/c ratio are significant. 1. Introduction Superplasticizers are often added during the mixing stage of concrete in small quantities related to the mass of cement to increase the fluidity of fresh concrete, increase strength, and prolong durability of hardened concrete. Researches have shown that compatibility of cement and superplasticizers is influenced by factors as the content of C3A and C4AF phase in PC clinker, total alkali amount, cement fineness, and the type and the amount of calcium sulfate [1]. Compatibility problems between superplasticizers and cement have been reported and these may be characterized by the fluidity of cement paste and its loss with time [2, 3]. Superplasticizer addition decreases the yield value of the paste close to zero, but the plasticity does not decrease significantly [4]. Naphthalene sulfonate superplasticizer is often used to improve the rheology of fresh concrete [5]. Termkhajornkit and Nawa [4] have reported in their work that the surface potential of fly ash differed from ordinary Portland cement (OPC) in both sign and value, and thus this is the reason for fly ash-cement paste flocculation. When naphthalene sulfonate superplasticizer was introduced into the fly ash-cement paste, the signs were the same and therefore dispersed well due to higher potential barrier. Adsorption of naphthalene sulfonate superplasticizers to the surface of cement particles changed the zeta potential of the particle surface to negative and thus increased the absolute value [6, 7]. The fluidity of sawdust ash-cement paste has not been reported. In this study, it was considered necessary to determine firstly the rheological properties of cement mortar using naphthalene sulfonate superplasticizer and secondly the influence of SDA and its compatibility on flow properties. Sawdust ash (SDA) was obtained from burning of timber wastes