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Asseily S.E.,Holderchem Building Chemicals
American Concrete Institute, ACI Special Publication | Year: 2015

The impact of clinker grinding aids (GAs) based on amine, glycol, or phenol on static yield stress (τ0) of cement pastes is not well understood. Results obtained from this project have shown that GA molecules remain active after the grinding process and provide variations in cement properties, whether in the fresh or hardened states. Flowability improved and τ0 decreased when the cement is ground using increased GA concentrations. This was attributed to the adsorption of these molecules onto the cement grains and saturation of surface charges, thus creating repulsive forces between neighboring particles. The decrease in τ0 was particularly pronounced when phenol-based GA was used, given the presence of polycarboxylate polymers that help dispersing cement particles upon mixing with water.

Assaad J.J.,Holderchem Building Chemicals | Harb J.,Notre Dame University - Louaize | Maalouf Y.,Notre Dame University - Louaize
Journal of Non-Newtonian Fluid Mechanics | Year: 2014

The direct shear test is widely used in soil mechanics to determine the cohesion (C) and angle of internal friction (ϕ). This paper aims to assess the suitability of this test to evaluate yield stress (τ0) of cement pastes having different flowability levels. Special emphasis was taken to eliminate friction between shear boxes, thus allowing the measurement of C ranging from several kPa to just a few Pa. Tests have shown that the maximum shearing stress prior to failure is not a material constant, but rather varies with the normal stress as per the Mohr-Coulomb law. Good correlations between C and τ0 determined using the vane method were established. Nevertheless, the vane method was found to over-estimate τ0 when the blades are positioned inside the specimen, particularly for cohesive materials. © 2014 Elsevier B.V.

Assaad J.J.,Holderchem Building Chemicals
Advances in Materials Science and Engineering | Year: 2015

The evaluation of grinding aid (GA) effect on clinker processing in laboratory grinding mills is relatively simple. Yet, the results obtained cannot be directly transposed to industrial mills, given the fundamentally different operational modes and grinding parameters. This paper seeks to evaluate the scale effect by comparing the results obtained from a closed-circuit tube mill operating at 90 ton/hr to those determined using a 50-liter laboratory mill. Tests results have shown that the decrease in specific energy consumption (Ec) due to glycol or amine-based GA can be evaluated under laboratory conditions. However, such tests underestimate the actual performance that could be achieved in real-scale mills; the Ec reduction due to GA is around twofold higher when grinding is performed in real-scale mill. Compared to industrial tests, the cement particle size distribution curves widened and shifted towards higher diameters when grinding was performed under laboratory conditions, particularly with GA additions. This led to remarkable changes in water demand, setting time, and 1- and 28-day compressive strengths. © 2015 Joseph Jean Assaad.

Issa C.A.,Lebanese American University | Assaad J.J.,Holderchem Building Chemicals
Materials and Structures/Materiaux et Constructions | Year: 2014

This research project is undertaken to assess the effect of washout loss on the drop in bond properties of reinforcing steel bars embedded in underwater concrete (UWC). Special emphasis was placed to evaluate bond using the same concrete mixtures that were subjected to washout. Testing was realized using the beam-end specimen method, and parameters evaluated included level of washout loss, bar diameter, and concrete cover. Test results showed that bond between steel and UWC is affected by the level of washout loss, which in turn is directly influenced by the mixture composition. Similarly to bond in concrete cast and consolidated above water, the ultimate UWC bond strength increases for smaller bar diameters and higher confinement reflected by increased concrete covers. UWC mixtures with increased washout losses exhibited higher drops in compressive, tensile, and bond strengths, as compared to concrete cast above water. Two boxes depending on the level of washout loss, i.e. from 4.2 to 6.9 % and from 8.8 to 10.8 %, have been proposed to predict the extent of bond decrease in UWC mixtures. © 2014 RILEM.

Assaad J.J.,Holderchem Building Chemicals
Minerals Engineering | Year: 2015

The effect of clinker grinding aids (GAs) on mill performance and cement properties is currently quantified in real-scale grinding plants. In fact, laboratory-grinding mills operated for given time interval do not consider the effect of circulating load, thereby leading to increased specific energy consumption (Ec) with excessively wide cement particle size distribution (PSD) curves. The main objective of this paper is to develop and validate a laboratory locked-cycle approach that mimics the industrial grinding operations occurring in closed-circuit tube mills. Test results have shown that Ec and its rate of decrease due to GA additions can be adequately predicted using this approach, when compared to those resulting from a real mill operating at 90 ton/h. The addition of GA led to narrower PSD curves and shifting towards smaller diameters, just like what happens in industrial grinding. Also, the cement properties including water demand, setting time, and compressive strength matched to a large extent within each other. © 2015 Elsevier Ltd. All rights reserved.

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