Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques

The objective of this study is to link the molecular structure of polycarboxylate-ether-type superplasticizers with the performance of cementitious systems in order to develop new products with enhanced properties, e.g. improved water reduction with a wide range of cements or a reduced retardation of cement hydration. Different experimental superplasticizers have been synthesized varying length and density of the polyether chains as well as the molecular weight of the polymer. The influence of these polymers on the properties of cement pastes and mortars was determined using various characterization methods like mortar flow, rheological and calorimetric measurements, adsorption measurements and mortar compressive strength. Characteristic connections between molecular structure of the polycarboxylate-type water reducers, adsorption behaviour, workability and retarding effect have been determined allowing the synthesis of new superplasticizers with improved performance.

Effects of the molecular architecture of comb-shaped superplasticizers on their performance in cementitious systems

Degradation mechanisms of natural fiber in the matrix of cement composites

Effect of ultrasonication energy on engineering properties of carbon nanotube reinforced cement pastes

This paper reports on the use of nano-SiO2 (nS) and nano-TiO2 (nT) in cement pastes and mortars. Samples with 0–3 wt.% nS, 0–12 wt.% nT and 0.5 water/binder weight ratio were prepared. Rheological and flow table measurements were carried out. In addition, the design of experiments was applied to validate the results found. The temperature of hydration and compressive strength with 28 days was also determined. In general, mortars exhibited noticeable differences in the rheological behavior, but less evident in temperature of hydration and compressive strength. The values of torque, yield stress and plastic viscosity of mortars with nanoadditives increased significantly, reducing the open testing time in rheology tests. Meanwhile, the flow table values reduced. In addition, spread on table and initial yield stress exhibited a power correlation, while the spread on table and plastic viscosity did not show any special relationship. The results of kinetics of hydration followed the same tendency found by rheology, in which samples with higher amounts of nS and nT showed remarkable changes in relation to the samples without nanoadditives. Mechanical properties were not significantly affected by nanoparticles in the range considered in this work.

Effect of nano-SiO2 and nano-TiO2 addition on the rheological behavior and the hardened properties of cement mortars

A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C—S—H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.

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Polycarboxylate superplasticiser admixtures: effect on hydration, microstructure and rheological behaviour in cement pastes

Behaviour of Repair Lime Mortars by Wet Deposition Process

Influence of SO2 deposition on cement mortar hydration

Effect of Dry Deposition of Pollutants on the Degradation of Lime Mortars with Sepiolite

The reaction of portland cement mortars with SO 2 gaseous pollutant and artificial 'acid rain' solution has been examined using laboratory exposure chambers, with realistic presentation rates of pollutants. The mortar were previously carbonated to produce superficial carbonation. Two mortars with different w/c ratio and hence specific surface were prepared and exposed into the chambers.
For dry deposition of SO 2 pollutant gas, the important roles of water and water plus oxidant in increasing chemical reaction are readily revealed. Further, accessible porosity also increases reaction through increased times of reaction of pollutant with the mortars. Interestingly, in the absence of deliberate surface wetting, the presence of oxidant, ozone, leads to a reduction in the already limited extent of reaction. Wet deposition studies using artificial 'acid rain' solution result in gypsum formation, which is more extensive for mortars of increased w/c ratios.

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S. Martínez-Ramírez

Papers

Polycarboxylate superplasticiser admixtures: effect on hydration, microstructure and rheological behaviour in cement pastes

Behaviour of Repair Lime Mortars by Wet Deposition Process

Influence of SO2 deposition on cement mortar hydration

Effect of Dry Deposition of Pollutants on the Degradation of Lime Mortars with Sepiolite

Deterioro de morteros de cemento producido por la "deposición" seca y húmeda de contaminantes atmosféricos