DOI: 10.14457/tu.the.2020.1034
title: Development of special concretes: underwater concrete, low binder self-compacting concrete and dry-cast steel fiber concrete

description: The aims of this thesis are to study effects and advantages of viscosity modifying agents (VMAs) on 2 types of high viscosity concrete such as self-compacting concrete and underwater concrete emphasizing on fresh concrete properties and study dry-cast steel fiber concrete (DCSFC). Viscosity modifying agents (VMAs) were used in self-compacting concrete and underwater concrete to improve their freshproperties such as workability (deformability, segregation resistance and passing ability). Some hardened properties of the concrete in term of durability are also investigated. This research also introduces a development of suitable mix proportion of dry-cast steel fiber concrete (DCSFC) for jacking pipes and also reports a series of tests on the dry-cast prism beams. For self-compacting concrete, this research is aimed to be a preliminary study of using tapioca starch as a viscosity modifying agent (VMA) for self-compacting concrete (SCC). The effect of tapioca starch on viscosity of SCC was investigated from the workability of corresponding mortars. Cement-only mortars with water to cement ratios (w/c) of 0.25 to 0.48, superplasticizer dosages of 1% to 2.5%, starch concentrations of 0%, 0.25% and 0.5%, were tested for workability. Mortar mixes that had an equivalent workability (flow diameter of 250 mm, and funnel flow time of 5 seconds) for each starch concentration were identified and checked for concrete properties. SCC mixtures were then tested for initial slump flow, slump flow loss, bleeding, setting times, and compressive strength. The results show that all tested concrete mixes provide equivalent initial workability, however the mixes with higher starch concentrations exhibit slower loss. For setting times, mixes with higher starch concentrations demonstrate longer setting times. Compressive strength of starch concretes, which always have higher water to cement ratio (w/c) than the non-starch concrete mixtures, are lower than that of the concrete without starch as their initial slumps were controlled to be the same in this experiment. However, their strengths are higher than or at least comparable to the strength range mostly used for conventional concrete. For Underwater concrete, this research aims to develop an anti-washout underwater concrete (here-in-after called underwater concrete) that can be cast in water without washout of powder particles by water. The underwater concrete was developed following self-compacting concrete (SCC) method but included the anti-washout property. For preliminary study, the underwater concrete was investigated by starting from the evaluation of anti-washout ability of cement-only mortars and cement mortars with fly ash by visual method with sand to mortar ratios (S/M) of 0.3 to 0.35, water to binder ratios (w/b) of 0.3 to 0.4. For VMA, this project used 2 codes of extra high-performance thickeners (VMA) which were Mighty VT100A&B and Mighty VT200 with dosages of 4 to 9% and 2 to 5%, respectively, and a superplasticizer (PC based) with the dosages of 1.5 to 2%. The mortars achieving anti-washout ability were used to design concrete mixes with the same sand to mortar ratios (S/M) and water to binder ratios (w/b) but the amounts of both VMAs and superplasticizer were increased (Mighty VT100A&B with a dosage of 10 %, VT200 with a dosage of 7 % and SP with dosages of 2 to 2.5 %) in order to achieve anti-washout ability and workability (slump flow of 650 to 750 mm, V-funnel time of 60 to 80 sec) and to achieve static segregation resistance before setting time (22 - 24 hrs.) and L-box tested with water filled in the box (passing ability under water). This underwater concrete was developed for a repair project of the port authority of Thailand at Samut Prakan province where marine environment conditions such as chloride resistance, sulfate resistance and non-shrink ability must also be considered, and these were achieved by applying 10 % of fly ash in the binder and 30 kg/m3of expansive agent in the concrete. As mixing process of the concrete caused entrapped air of about 8-12 %, a de-air admixture was used to reduce the entrapped air to prevent viscosity loss and settlement of the concrete due to the high content of entrapped air.For Steel fiber-reinforced concrete (SFRC), this research aims to be a preliminary study and develop