S.M.A. El-Gamal

Physico-chemical characteristics of blended cement pastes containing electric arc furnace slag with and without silica fume

Abstract Filled-pozzolanic cement pastes were made by different replacements of OPC by electric arc furnace slag (EAFS) with silica fume (SF) at water/cement ratio of 0.27. The pastes were hydrated up to 90 days. At each time interval, the physico-chemical characteristics of the hardened cement pastes were studied and related to the structure of the hardened pastes and the role of EAFS replacement as a filler in the hardened OPC-EAFS pastes. It was found that the optimum replacement of OPC by EAFS for the improvement in hydraulic properties of filled cement pastes is 6%. High replacement of OPC by EAFS (10% or 15%) causes a notable deterioration in the compressive strength at all ages of hydration. The replacement of EAFS in Mix (90% OPC + 10% EAFS) by 4% SF causes a marked improvement in the mechanical properties for the hardened pastes of Mix (90% OPC + 6% EAFS + 4% SF). The DSC thermograms for all pastes indicated the formation of nearly amorphous calcium silicate hydrates, calcium sulphoaluminate hydrates, calcium aluminate hydrates and portlandite. The SEM micrographs showed that the partial substitution of OPC by EAFS and/or SF leads to more dense structures as compared to the neat OPC paste.

Hydration characteristics and compressive strength of hardened cement pastes containing nano-metakaolin

Abstract In this study the effect of inclusion of nano-metakaolin (NMK) to ordinary Portland cement (OPC) on the hydration characteristics and microstructure of hardened OPC–NMK pastes was studied. The OPC–NMK blends were prepared by the partial substitution of OPC by NMK (4, 6, 10 and 15 weight %). The fresh pastes were made using an initial water/solid (W/S) ratio of 0.27 by weight and then hydrated for various time intervals. At the end of each hydration time, the hardened blended cement pastes were tested for compressive strength, free lime content, combined water content, X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The compressive strength results revealed that the inclusion of nano-metakaolin into OPC improved the mechanical properties of NMK–OPC pastes during almost all ages of hydration, especially with the paste containing 10 wt% NMK. The compressive strength values obtained for OPC paste blended with 4% silica fume (SF) and 6% NMK are comparable to those of the neat OPC paste. The DSC thermograms and XRD diffractograms obtained for some selected hardened pastes indicated the formation of amorphous calcium silicate hydrates, calcium sulfoaluminate hydrates, calcium aluminate hydrate and calcium hydroxide. SEM micrographs showed the formation of a dense microstructure for the hardened OPC–NMK and OPC–NMK-SF pastes as compared to the neat OPC paste after 90 days of hydration.

Characteristics of lime-silica fume mixtures

The hydration of two calcium hydroxide-silica fume mixtures was studied at 25°C. The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiO2 and H2O/SiO2 molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis. The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO2 and H2O/SiO2 in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.

Early hydration characteristics of oil well cement pastes admixed with newly prepared organic admixture

Abstract A number of chemical and mineral admixtures are usually used in the oil-well cement (OWC) pastes to modify and control their fluidity to resist the higher temperatures and pressures during the drilling process of the well. In this study a newly prepared aliphatic organic compound namely cyclohexanone glyoxylate condensate (CG) was synthesized. The prepared compound (CG) was characterized using Fourier Transition Infrared spectroscopy (FT-IR) and microanalysis of carbon, hydrogen, oxygen and sulfur elemental analysis techniques. The effect of additions of 0.25, 0.50, 0.75 and 1 (mass%) of this admixture on the mechanical and early hydration characteristics of OWC pastes was studied. The phase composition for some selected hardened specimens was investigated using X-ray diffraction (XRD) and thermogravemtic analysis (DTGA) techniques. The results indicated that, addition of cyclohexanone glyoxylate condensate (CG) admixture to OWC pastes causes a slight retardation for the early rate of hydration of OWC. Addition of 0.25% of CG to OWC causes a slight improvement in the compressive strength values during nearly all ages of hydrations. XRD and DTGA results for the neat and CG admixed OWC pastes, indicate that the main hydration products are nearly amorphous calcium silicate hydrates (mainly as CSH-I and CSH-II), calcium sulfoaluminate hydrates (ettringite and monosulfate hydrate) as well as portlandite (CH).

Utilization of OPC-Pumice composites for efficient heavy metals removal

ABSTRACT The immobilization effect of 1 and 3 mass % of Ni2+ or Co2+ ions on the hydration reaction of ordinary Portland cement (OPC) and ordinary Portland cement blended with 5 and 15 mass % pumice was investigated. This was done by studying the bulk density, total porosity, compressive strength as well as identifying the phase composition of the formed hydrates using X-ray diffraction (XRD) technique. In addition, leaching behaviour of Ni2+ and Co2+ ions was examined up to 90 days using static leaching technique. The results indicated that the incorporation of these ions causes a notable retardation for the early hydration of the OPC. This effect is more noticeable in presence cobalt ions. Besides, the retarding effect was increased by increasing the percentage of heavy metal ions incorporated in the hydrated matrix. However, for OPC-pumice blended cement pastes, the existence of Ni2+ or Co2+ ions resulted in an enhancement in the compressive strength values during the hydration period from 3-28 days to be comparable with the values of neat OPC pastes. This enhancement is attributed to the interaction of these ions with pumice which increases the heavy metal fixation.