Mohamed Heikal

Limestone-filled pozzolanic cement

Fillers are specially selected, natural or artificial inorganic materials, which improve the physico-chemical and mechanical properties of the cement such as workability or water retention. They can be inert or have slightly hydraulic, latent hydraulic or pozzolanic properties. They cause no appreciable increase of the water demand of the cement, in addition to not impairing the resistance of the concrete or mortar to deterioration in any way or reducing the corrosion protection of reinforcement. Fillers are normally either limestone or any inert material such as sand. The aim of this investigation is to study the effect of substitution of limestone for Homra in pozzolanic cement. The effect of limestone replacement was studied by the determination of the combined water, free lime contents, bulk density, total porosity and compressive strength. The results show that the addition of limestone reduces the initial and final setting time, as well as total porosity, whereas the free lime and combined water increase with limestone content. It can be concluded that limestone fills the pores between cement particles due to formation of carboaluminate, which may accelerate the setting of cement pastes.

Effect of temperature on the physico-mechanical and mineralogical properties of Homra pozzolanic cement pastes

Abstract The effect of temperature on the phase composition and physico-mechanical properties of cement pastes is vital for fire resistance. Addition of fine, divided materials, such as dehydrated aluminum silicate (fired clay), natural hydrated aluminum silicate (clay), chromite, sintered magnesite, slag, silica, fly ash, diatomaceous earth, and Homra (crushed clay bricks), to Portland cement is known to increase heat resistance by combining with lime. Homra is a pozzolanic material that can react with lime liberated from the hydration of ordinary Portland cement (OPC). This reaction improves the microstructure of cement pastes. In this study, OPC was partially substituted by Homra in the ratios of 10, 20, and 30 wt.%. The cement pastes were fired for 3 h without any load at increasing temperatures from 100°C to 600°C by increment of 100°C. The results show that the replacement of OPC by 20 wt.% Homra improves the compressive strength by about 25.0%, but replacement by 10 and 30 wt.%, the strength increases by 4.0% and 8.5% at 600°C. This result is also due to the pozzolanic reaction of Homra with liberated lime to produce additional amounts of calcium silicate hydrates.

Portland cement clinker, granulated slag and by-pass cement dust composites

Three blends of slag cement were prepared, namely 70/30, 50/50 and 30/70 mass% of Portland cement clinker and granulated slag, respectively. Each blend was mixed with 2.5, 5.0, 7.5 and 10.0 mass% by-pass cement dust. The physical properties of cement pastes were studied, including setting times, electrical conductivity and fluidity. The results indicated that the rheological properties of Portland cement clinker were enhanced by partial replacement by granulated slag. By-pass cement dust affects the rheological properties of Portland cement clinker/granulated slag composites and depends on its amount as well as mix composition. The increase in the amount of by-pass cement dust increases the required water of normal consistency. The setting time of Portland slag cement paste was extended with the increase in slag content. The addition of 2.5 mass% by-pass cement dust to M.1 (70 mass% Portland cement clinker/30 mass% granulated slag) and M.2 (50 mass% Portland cement clinker/50 mass% granulated slag) retards the initial and final setting time, whereas it accelerates the final setting time of M.3 (30 mass% Portland cement clinker/70 mass% granulated slag). The presence of by-pass cement dust affects the location and height of the conductivity peaks. By increasing the by-pass cement dust from 2.5 to 7.5 mass%, the conductivity maximum increases. With further addition (10.0 mass%), the height of the conductivity maximum decreases.

Physico-chemical characteristics of some polymer cement composites

The electrical conductivity of cement pastes can give an indication of the initial hydration of the cement pastes and early formation of products. In this study, sulphate-resisting cement (SRC) pastes were prepared with different doses of two synthesised admixtures, namely phenol formaldehyde sulphonate (PhFS) and melamine formaldehyde sulphonate (MFS). This work is aimed to evaluate the effect of PhFS and MFS on the hydration reaction of cement pastes during the first 24 h by determining the initial, final setting times and the electrical conductivity changes, as well as the effect of these polymers on the hydration progressing up to 90 days by determining the chemically combined water content and gel/space ratio of each paste at different intervals of time (1, 3, 7, 28 and 90 days).

Coupled Effect of Elevated Temperature and Cooling Conditions on the Properties of Ground Clay Brick Mortars

Abstract When a concrete structure is exposed to fire and cooling, some deterioration in its chemical resistivity and mechanical properties takes place. This deterioration can reach a level at which the structure may have to be thoroughly renovated or completely replaced. In this investigation, four types of cement mortars, ground clay bricks (GCB)/sand namely 0/3, 1/2, 2/1 and 3/0, were used. Three different cement contents were used: 350, 400 and 450 kg/m3. All the mortars were prepared and cured in tap water for 3 months and then kept in laboratory atmospheric conditions up to 6 months. The specimens were subjected to elevated temperatures up to 700°C for 3h and then cooled by three different conditions: water, furnace, and air cooling. The results show that all the mortars subjected to fire, irrespective of cooling mode, suffered a significant reduction in compressive strength. However, the mortars cooled in air exhibited a relativity higher reduction in compressive strength rather than those water or furnace cooled. The mortars containing GCB/sand (3/0) and GCB/sand (1/2) exhibited a relatively higher thermal stability than the others.

Unilateral surgically induced Necrotizing Scleritis after trabeculectomy with Ologen in a patient with pigmentary glaucoma

Purpose In this report we record the first surgically induced Necrotizing Scleritis case related to trabeculectomy with the use of Ologen Collagen Matrix Implant. Observations Surgically induced Necrotizing Scleritis is a rare pathological entity that complicates ocular (sclera) surgery. Conclusions and importance Prompt management of surgically induced Necrotizing Scleritis related to trabeculectomy with the use of Ologen and close follow up is very important to prevent its destructive nature on the globe.

Effect of Various Superplasticizers on the Textural Properties of Silica Fume Pozzolanic Cements

The influence of different superplasticizers on the hydration and textural characteristics of hardened pozzolanic cement pastes was evaluated. Thus, the BET surface areas and pore structures of hardened cement pastes containing different amounts of silica fume and/or various superplasticizers were determined via nitrogen adsorption isotherms measured at −196°C. Three types of superplasticizers were used in this study, viz. naphthalene formaldehyde sulphonate (NFS), sodium gluconate (SG) and their mixtures (NFS + SG). The various phase compositions and microstructures were assessed by X-ray diffraction (XRD) and scanning electron microscope (SEM) studies. The results revealed that the specific surface area (SBET) of the hardened cement pastes decreased as the amount of silica fume increased and also on addition of superplasticizer. The decrease in surface area was more pronounced in the presence of 30 wt% silica fume as well as with superplasticizers. Thus, the maximum decrease in the SBET value due to the addition of 4% NFS superplasticizer attained values in the range 46–68%. In addition, increasing the curing time from 3 d up to 180 d decreased the surface area of the pure and superplasticized cement pastes. The decrease in SBET for the various cement pastes could be attributed to the pozzolanic activity of the silica fume with a subsequent increase in the amount of hydration products within the pore system.