An Experimental Study of Effects of Superplasticizer on Fresh and Hardened Properties of Concrete
This paper presents the results of an experimental research on the workability and compressive strength of ordinary and standard concrete. Superplasticizers are commonly known as High Range Water Reducers (HRWRs) because it permits low water cement ratio as well as the workability also affected. In this paper the properties of concrete mixtures with three different dosages of superplasticizers SNF have been investigated. In this experimental programme superplasticizer Sikament®170(SWP) of basically modified naphthalene/melamine formaldehyde sulphonate dispersion and having brown liquid confirming to IS: 91031999 & IS: 2645, ASTM C 494/C494M, Type F has been used. The properties investigated are workability on the fresh state and compressive strength on the hardened state of concrete by using three mixes with three superplasticizer dosages (0.2%, 0.4% and 0.6%) is used. Various concrete mixes (M-20, M-30 and M-40) are design by IS 10262:2009, Concrete Mix Proportioning Guidelines. Compressive strength at 7 and 28 days was also determined. The graphs between different percentage of superplasticizers with W/C ratio and compressive strength are plotted. Overall 72 specimens (concrete cube) with the dimension of 150 mm x 150 mm x 150 mm were fabricated at laboratory.
MODERN BUILDING MATERIALS, STRUCTURES AND TECHNIQUES
The family of iterative methods for static and natural vibration analysis, based on preconditioned conjugate gradient (PCG) method with aggregation multilevel preconditioning, is considered. Both: the element-by-element procedure for assembling of stiffness matrix and sparse direct solver for it factoring and fast forward − backward substitutions ensure the high stability of methods against ill-conditioning. The generalized preconditioned conjugate gradient method with shifts in aggregation multilevel preconditioning is developed to overcome the lock of convergence, which is met when conventional PCG methods are applied for eigenvalue analysis.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.