The Effect of Using Commercial Red and Black Iron Oxides as a Concrete Admixtures on its Physiochemical and Mechanical Properties

Study discuss the effect of using commercial red and black iron oxides (RIO and BIO) as a concrete admixtures in percentages do not exceeded 2.5% of each oxide from the amount of cement, this study tested the effect of every portion from each oxide at different ages on the compressive strength as well as the workability represented as a values of slump. We conclude that the optimum portion of RIO is 2.5%, but for BIO is 1%, while the proposed uses of RIO in concrete technology are retarder through slump increment reach to 50%, coloring material and mineral admixture through Compressive Strength increment (7-365 days) 5.5-12.8%. On the other hand BIO will propose as, coloring material and mineral admixture through Compressive Strength increment (7-365 days) 22.2-30.8%. SEM-images are clearly show the formation of Calcium hydroxide phase at 7-days while at 1-year the CSH phase is a predominate one, in both cases of RIO and BIO. XRD-pattern is supported the results outcomes through SEM-images

Effect of sulphate, chloride and elevated temperature on the properties of Egyptian slag binder

The present research aims to explain the physico-chemical and mechanical characteristics of alkali activated slag geopolymer binder (AASGB). Commercial sodium hydroxide (SH) and sodium silicate liquid (SSL) are utilized as an alkaline activator at different temperature namely 25oC and 65oC. The hydration characteristics and physico-mechanical properties are illustrated through the determination of combined water contents Wn), combined slag, total porosity (TP), compressive strength (CS), bulk density (BD) and XRD analysis as spectroscopic tools upto 180 days. The durability of the AASGB against aggressive ions (sulphate and chloride ions ) as well as effect of elevated temperatures upto 1000oC are studied. The activated binders are immersed under 5% MgSO4 and/or 5%MgCl2 solutions upto12 months. The data showed that the higher concentration of SH (1mol/kg) at 65oC exhibited the highest resistance to elevated temperature upto 1000oC as well as given a high resistance against sulphate and chloride attack

Effect of Alkali Concentration on Physico -Chemical and Mechanical Properties of Slag Based Geopolymer Cement.

In this article we studied the effects of sodium hydroxide pellets (SH) and sodium silicate liquid (SSL) as an activator on the physico chemical and mechanical Properties of ground granulated blast furnace slag (GGBFS) geopolymer pastes. Various mixes are prepared using different liquid/solid ratios (L/S) by weight. The hydration characteristics of the various mixes have been tested through determination of total porosity, compressive strength, bulk density, chemically combined water, and XRD analysis at different time intervals from 2 days up to 90 days under relative humidity 100%. The results elucidated that as the quantity of alkali activator increases up to (15% SSL, and 15% SH), the compressive strength increases up to 90 days. The combined water content of all mixes increases up to 90 days. Also the bulk density raises and the total porosity minimizes, this is due to the addition of the pozzolanic materials. All mixes showed good stability of its compressive strength values in 5 % MgSO4 solution. The data showed that mix S6 (100% GGBFS) activated by (15% SSL, and 15% SH) is the most appropriate binding material (geopolymer cement) that has good properties so it can be used as alternative binding materials to the ordinary Portland cement

HYDRATION CHARACTERISTICS OF PROMPT CEMENT IN THE PRESENCE CITRIC ACID AS RETARDER

The aim of the present work is to study the influence of citric acid (CA) as retarder on the properties of prompt cement pastes. The dosages of CA were 0.50, and 0.75, 1.00 and 1.25 mass % of prompt cement. The initial and final setting times, bulk density, compressive strength, total porosity, and hydration kinetics such as free lime, combined water contents and XRD for selected sample were investigated. The results obtained in this study showed that the addition of CA elongates the initial and final setting times and decreases the compressive strength and combined water contents, whereas, it increases the total porosity at all ages of hydration. CA retards the liberation of Ca(OH)2 of prompt pastes. The free lime contents of prompt cement pastes are slightly increased up to 28 days then sharply increased up to 90 days. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution. The sharp increase of compressive strength at later ages after 28 days up to 90 days. The presence of 0.75 mass % citric acid achieves the initial and final setting time of the prompt cement according to the ASTM specification

Hydrothermal synthesis of calcium silicate hydrates in the presence of <em>3d-</em>ferromagnetic cations

1098-1101The effect of-transition metal cations, Fe3+ , Co2+ and Ni2+ on the formation of calcium silicate hydrates CaO&middot;SiO2&middot;H2O in the reaction system has been studied. The hydrothermal reaction products have been examined by X-ray diffraction, infrared spectroscopy and atomic absorption spectrophotometric techniques. The results indicate the presence of different shifts in the main interlayer d-spacing of calcium silicate hydrate hydrothermal products, especially 11 &Aring;-tobermorites: 5CaO&middot;6SiO25H2O. Calcium silicate hydrate phases formed are affected by ionic radii, acidic radical, concentration of the concerned cations and the reaction time. The mechanism of the reaction and incorporation (or substitution) of these cations in the crystal lattice of calcium silicate hydrate phases is also discussed

Effect of Calcium Chloride on the Hydration Characteristics of Ground Clay Bricks Cement Pastes

Effect of CaCl2 on the hydration characteristics of the different cement pastes using ordinary Portland cement (OPC) and blended Portland cement with ground clay bricks (GCB) was studied. Various mixes were prepared using a water/solid ratio (W/S) of 0.25 (by weight). Three percentages of CaCl2 (0.25, 0.5 and 0.75%) are used; the CaCl2 used was dissolved in the mixing water. The hydration characteristics were tested via the determination of the combined water content, phase composition, compressive strength, total porosity (P%) and X-ray diffraction analysis (XRD) at different time intervals up to 180 days. The results showed that calcium chloride accelerates cement hydration in all systems studied. Ten % GCB in the presence of 0.50 % CaCl2 is the optimum ratio which has the higher compressive strength. Key words: Blended Portland cement; calcium chloride; ground clay bricks; hydration cemen

Hydrothermal synthesis of calcium silicate hydrates in the presence of <em>3d-</em>ferromagnetic cations

1098-1101The effect of-transition metal cations, Fe3+ , Co2+ and Ni2+ on the formation of calcium silicate hydrates CaO&middot;SiO2&middot;H2O in the reaction system has been studied. The hydrothermal reaction products have been examined by X-ray diffraction, infrared spectroscopy and atomic absorption spectrophotometric techniques. The results indicate the presence of different shifts in the main interlayer d-spacing of calcium silicate hydrate hydrothermal products, especially 11 &Aring;-tobermorites: 5CaO&middot;6SiO25H2O. Calcium silicate hydrate phases formed are affected by ionic radii, acidic radical, concentration of the concerned cations and the reaction time. The mechanism of the reaction and incorporation (or substitution) of these cations in the crystal lattice of calcium silicate hydrate phases is also discussed

Inertization of lead by using blended cement pastes

Inertization of lead nitrate Pb(NO3)2, a representative of soluble lead compound, with five cements pastes based on either ordinary Portland cement (OPC) or blended Portland cement with granulated blast-furnace slag (GBFS) or metakaolin (MK) was studied. Various mixes were prepared by using a water/solid ratio (W/S) of 0.28 (by weight). Two ratios of Pb ions (1.0% and 2.0% of the solid binder) was used by adding to the mixing water. Hydration characteristics of the different cement pastes were investigated via the examination of chemically combined water content, compressive strength, X-ray diffraction analysis and thermal analysis (DTA/TGA). Leaching of lead ions from various hardened cement pastes was examined. The results showed that lead nitrate retards cement hydration through the formation of plumbate salt CaPbO3. The obtained results of leaching showed a high degree of immobilization of Pb ions in the various cement pastes. Moreover, partial replacement of Portland cement by MK is more efficient than granulated blast-furnace slag GBFS

Effect of nano-SiO2 (NS) on dolomite concrete towards alkali silica reaction

The aim of this work was to study the effect of nano silica on the physico-mechanical properties of concrete containing dolomite coarse aggregate and its effect on alkali silica reaction. In this work, Portland cement is replaced by 1, 2 and 4 wt.% nano silica (NS). It is clear that nano silica up to 2 wt.% leads to increase the compressive strength and decrease the total porosity up to 180 days of curing in tap water. This is due to that nano silica content acts as pozzolanic material and nucleating sites for the hydration products, which enhances the cement hydration rate. A 4 wt.% NS led to reduce the mechanical properties but is still higher than dolomite control because it leads to coating of the cement grains, retarding its hydration rate and therefore, decreases the hydration products formation. The resistivity of dolomite concrete control against 1 N NaOH up to 6 months of immersion has been carried out. The results show that all concrete mixes have high resistivity towards 1 N NaOH up to 6 months of immersion. The compressive strength development rate of dolomite concrete control containing 2 wt.% of nano silica is higher than that of control. This is due to the continuous activation and accumulation of hydration products. This indicates that the NaOH has marginal compacts on the mechanical properties reduction, and this result confirmed that dolomite aggregate has higher resistivity to alkali silica reaction. XRD and SEM photograph are applied to investigate the formed hydration products. Keywords: Dolomite concrete, Compressive strength, Alkali silica reaction, Nano silica, Total porosit