Study On Preparation Of High Salt-resistance Ultra- High Strength Concrete Without Coarse Aggregate

At present, the lack of durability and the problem of poor salt resistance of concrete are generally faced with, especially for the concrete used in the Marine. Due to the lack of durability, concrete service life is shortened greatly, causing huge economic loss and waste of resources. So the study and preparation of a concrete with high strength and high salt resistance has the vital significance to marine concrete development and the construction of the ocean.This article, from the erosion mechanism of various salts on concrete, hydration reaction mechanism of mineral admixtures and salt resistance, combined with the basic principles of the preparation of ultra high strength concrete, selecting slag powder, silica fume and fly ash as mineral admixtures into composite gelled material preparation, use the high performance poly carboxylic acid water reducing agent powder to prepare high salt high strength concrete without coarse aggregate with a certain particle size of sand as fine aggregate.This study first prepared the composite gelled material with low clinker, high mineral admixtures and high fluidity, which can be used as a Marine special gelled material to directly prepare marine concrete. Then, with cement sand ratio of 1:1 and water cement ratio of 0.23, super-high strength concrete without coarse aggregate, compressive strength of over 100 MPa, is prepared, respectively employing fresh water, artificial seawater and 5% sodium sulfate solution to cure concrete. Using XRD and SEM, it made a research on the phase and morphology of hydration products and investigated the salt resistance through dry shrinkage of concrete, chloride ion permeability coefficient, water erosion coefficient and sulphate erosion coefficient. The results show that:(1) the optimum content of poly carboxylic acid water reducing agent is 0.2% of the gelled material quality;(2) the optimal mixing proportion of composite cementing material proportion is 45% cement, 40% GGBS, 5% silica fume, 10% fly ash, 28 d compressive strength of concrete of 110.3 MPa, flexural strength of 12.1 MPa;(3) using artificial seawater and sulfate solution to cure of concrete, the 28 d and 56 d compressive strength of the concrete is higher than that of curing with fresh water;(4) 3d compressive strength of concrete prepared with composite gelled material is lower than the pure cement concrete, and after 7d, its compressive strength surpass the latter, significantly increase the later strength;(5) the addition of composite gelled material can effectively improve the compressive strength and flexural strength of concrete;(6) in the concrete prepared with composite gelled material, both at 3d and 28 d, diffraction peak of XRD phase microcline content(KAlSi3O8) is obvious;(7) the addition of composite gelled material can effectively reduce the dry shrinkage of concrete, improve the ability to resist chloride ion, sulfate and seawater erosion.In this study, the prepared composite gelled material, mixing with poly carboxylic acid water reducing agent powder, suitable for industrial mass production, are used directly as the Marine engineering high-performance special cementing materials.The high salt high strength concrete without coarse aggregate prepared in this study, with the performance of the ultra-high strength and high salt resistance, has achieved the expected design goal and has important theoretical significance and practical value for the Marine engineering islands construction..