The Effects Of Particle Shape And Powder Content Of Manufactured Sand On The Properties Of Concrete

With the developing of large number of construction, a large amount of concrete is in need and natural sand(NS) has been in short supply. To seek a new fine aggregate is imperative. On the other hand, large-scale city update generates a lot of construction waste. How to handle the construction waste is also a difficult problem.Therefore, engineers try to use manufactured sand(MS) and recycled sand(RS) to solve the shortage of NS.MS and NS have some characteristics different from NS, such as composition,particle shape and surface roughness, grading, powder and so on. In addition, RS has a high rate of water absorption. These characteristics have a great impact on the performance of concrete. How to parameterize these characteristics and quantify the effect of them on the concrete is an important problem in engineering application.Therefore, a systemic research is needed. In this paper, the effects of particle shape and powder content of manufactured sand on the properties of concrete is mainly studied.In this paper, roundness(Rr), radius ratio(Rz) and aspect(Rd) were selected to represent the particle shape of fine aggregate. The results showed that the particle shape of 2.36 mm of fine aggregate was the most representative. With the increase of Rr, Rz and Rd, the workability of concrete would be worse and the mechanical properties would be better. However, at the micro level, the particle shape of fine aggregate has no direct effect on the width of interfacial transition zone(ITZ) of concrete. It shows that in these three parameters, Rz can represent the effect of the particle shape of fine aggregate on the performance of concrete better.Seeing that previous researchers focus on the research of limestone MS while neglecting the other lithologies, so granite MS was selected to research in this paper.Studies showed that there was a parabola relationship between the powder content ofgranite MS and the workability, mechanical properties and durability of concrete.Powder content had an optimum value. When the powder content was at the range of5~10%, the workability of concrete was the best. For the mechanical properties, the value was between 8% and 14%, and 12 ~ 14% for the dynamic elastic modulus,about 6% for the impermeability.In the research of the effect of granite powder on the cement hydration reaction,it showed that in first few hours, granite powder restrained the cement hydration. It made the rate of hydration exothermic slow down and the total heat release reduced;But a few hours later, it began to promote the cement hydration, accelerated the rate of hydration exothermic and increased the total heat release in 48 hours. Limestone powder had the opposite effects. It promotes the cement hydration reaction first and then restrains.After adding granite powder, no new substance formed in the hardened cement paste. But after adding limestone powder, calcium carboaluminate hydrate(Mc)emerged. So we can conclude that: granite powder is an inert filler and doesn’t participate in the cement hydration reaction; limestone powder has activity, can participate in the cement hydration reaction and produce Mc.