Pozzolanic Cement Pastes Research Articles

Manufacture of eco-friendly cementitious building materials of high performance from Egyptian industrial solid wastes

One of the goals of modern societal development is to achieve environmental sustainability by expanding the number of smart cities with eco-friendly buildings. A research was carried out to investigate the possibility of utilizing Egyptian industrial solid wastes from factories to create sustainable construction materials in order to accomplish this goal. Along with various waste products including cement kiln dust (CKD) and silica fume (SF), which were chemically categorized, the investigation identified metakaolin (MK) and dealuminated kaolin (DK). Various dry mixes were used to determine the hydration characteristics of the binders, including MK-CKD, DK-CKD, OPC-DK, DK-CKD-SF, MK-CKD-SF, and OPC-DK-SF.The physico-chemical and mechanical properties of the cement pastes were analyzed using compressive strength (CS), chemically combined water (Wn, %), and free lime (CaO, %) content over time. The hydration products were identified using differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM) analyses. The findings revealed that DK had a larger surface area (95 m2/g) than MK and displayed greater pozzolanic activity, particularly during early hydration. Moreover, the inclusion of SF provided further densification of the microstructure of the hardened DK-CKD-SF and/or OPC–DK–SF pastes.According to the findings, the OPC-DK pozzolanic cement pastes had a denser structure than the neat OPC paste. Moreover, the inclusion of SF resulted in additional densification of the microstructure of the hardened OPC-DK-SF pastes, which was evident in the observed increase in compressive strength values at all ages of hydration. The use of industrial solid waste as a sustainable building material has the potential to assist Egypt in meeting its goals for sustainable development and climate protection.

Effect of various plasticisers on viscous flow properties of natural pozzolanic cement pastes

The effect of various plasticisers (lignosulfonates and copolymers) on volcanic cement was assessed in this study. The volcanic cement was designed by substituting Portland cement with a natural volcanic pozzolan resulting from Andean volcanic activity. The best results (i.e. the volcanic cement pastes that showed shear-thickening viscous flow behaviour) were obtained when the zero-shear viscosity, minimum viscosity and shear rate for the onset of shear-thickening behaviour showed dependency on the paste concentration, Portland cement substitution and plasticiser concentration. The results were verified by the distorting effect of solid particles on the flow field.

Residual Capability of Alkali Binding by Hydrated Pozzolanic Cements in Long‐Service Concrete Structures

An experimental procedure was developed and applied to cement pastes made with two different pozzolanic cements (CEM IV/B (P) and CEM IV/B (V)) in order to ascertain the existence of a residual capability of alkali binding by long‐term hydrated pozzolanic cements and, at the same time, to evaluate the alkali retention capability and the concentration of OH− ions in the pore solution of such cementitious matrices. The developed procedure consisted of accelerated curing of cement paste specimens (150 days at 60°C and 100% RH), subsequent leaching tests at 60°C for 30 days by using deionized water or basic solutions (NaOH or KOH at different concentrations) as leaching media, and correlation of the leaching test results with a simple mass balance equation for sodium and potassium ions. The developed procedure was found to be appropriate for evaluating both the pore liquid alkalinity and the alkali retention capability by long‐term hydrated pozzolanic cement pastes. A residual capability of alkali binding was also identified for both tested pozzolanic cements, thus indicating their potential ability to prevent (CEM IV/B (V)) or minimize (CEM IV/B (P)) the risk of deleterious expansion associated with alkali‐aggregate reaction in long‐service concrete structures, like concrete dams.

Properties and performance of metakaolin pozzolanic cement pastes

Cement industry produces the 7% of the global CO2 emission. The most effective way to decrease CO2 emission of cement industry is the substitution of a proportion of cement with supplementary cementing materials. Metakaolin (MK) is a silica-based product that, on reaction with Ca(OH)2 (CH), produces C–S–H gel at ambient temperature. MK also contains alumina that reacts with CH to produce additional alumina-containing phases, including C4AH13, C2ASH8 and C3AH6. The aim of our research is to investigate the effect of MK up to 20 mass% substitutions of OPC on the hydration characteristics of MK-blended cement pastes. The physico-chemical properties of the hardened cement pastes were studied up to 90 days of hydration. The hydration products of some selected samples were investigated using XRD, DTA and TG techniques. The results indicated that substitution of up to 20 mass% OPC by MK as a pozzolanic materials resulted in an increase in the standard water of consistency, acceleration of the initial setting times, high compressive strength values at earlier ages and improvement of the mechanical, durability properties as well as performance of MK pozzolanic cement pastes.

Effect of substitution of blast-furnace slag by fired drinking water sludge on the properties of pozzolanic cement pastes

The effect of fired drinking water sludge (FDWS) as a mineral admixture on the physico-mechanical properties and the fire resistance of pozzolanic cement pastes has been investigated. Five blends of ordinary Portland cement, blast-furnace slag (GBFS) and FDWS were prepared. The Portland cement was fixed to 70 mass%, while granulated slag was replaced by 0, 3, 6, 9 and 12 mass% of fired sludge. The phase composition was identified using X-ray diffraction, thermal gravimetric analysis and differential scanning calorimetry. The results have shown an increase in the required water of standard consistency and elongation of setting times with increasing the fired sludge content. The bulk density has decreased with increasing the sludge content, while the compressive strength was enhanced at later ages for 3 and 6 mass% FDWS substitution. In addition, the specimen that contains 9 mass% FDWS gave the best firing resistance at high temperature, whereas Portland cement paste has been completely deteriorated at 800 °C.

Effect of hydrothermal curing on the hydration characteristics of artificial pozzolanic cement pastes placed in closed system

This paper describes the effect of high temperature on the hydration characteristics of artificial pozzolanic cement pastes containing metakaolin with or without silica fume for different hydrothermal ages in well closed stainless steel capsule. Pastes were hydrothermally treated in well closed stainless steel capsule at 180°C for different hydrothermal ages (2, 4, 6, 12 and 24h). Hydration characteristics of the hydrothermal OPC–MK–SF pastes were studied by the determination of compressive strength, bulk density, porosity and chemically combined water contents at different hydrothermal ages. The phase composition and morphology of the formed hydrates were studied using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Results indicated that the compressive strength of multi-blended mixes containing silica fume 5% is by mass higher than the corresponding Portland cement control at later age up to 6h of hydrothermal curing age.

Mechanical strength and corrosion detection of pozzolanic cement

Various pozzolanic cement pastes based on ordinary Portland cement (OPC), granulated blast furnace slag (GBFS) and metakaolin (MK) were studied. Mixes were prepared using a water/solid ratio (W/S) of 0.25wt.%. Hydration characteristics of the different hardened cement pastes were investigated via the examination of chemically-combined water content, compressive strength, and X-ray diffraction analysis under normal curing conditions at various time intervals up to 90days. Thermal analysis (DTA/TGA) was carried out for the mix containing 30% Mk and GBFS at 28days. The electrical conductivity was measured during the early stages of hydration for the various cement pastes at 30°C. Moreover, the corrosion potential of reinforced steel embedded in the metakaolin–slag–cement system was studied in comparison to their corresponding ordinary Portland cement, to evaluate the probability of steel corrosion. The results showed that the values of Wn% in these blended pastes are higher than blended pastes with slag or metakaolin only. Also, mix containing 70% OPC, 15% Mk and 15% GBFS has higher compressive strength and corrosion resistance than the net cement paste. The results of thermal analysis indicate that the presence of 30% GBFS and MK consumed the CH formed as a result of the hydration of OPC (pozzolanic reaction).

Physicochemical and Fire Resistance Characteristics of Artificial Pozzolanic Cement Pastes

THE PRESENT work describes details concerning preparation and ….. physico-chemical characterization of pozzolanic cement pastes . The prepared cement pastes were examined by using XRD, SEM and nitrogen adsorption at-196

Physico-chemical and mechanical characteristics of pozzolanic cement pastes and mortars hydrated at different curing temperatures

The effect of elevated curing temperature on the properties of cement mortars is vital for heat resistance. Addition of pozzolanas, such as slag, to type I cement is known to increase heat resistance. In this study, OPC was partially substituted by two types of slag (WCS and ACS) in the ratios of 10, 20, 30, 40 and 50 wt.%. The cement mortars were cured for 120 days at different curing temperature from 25 to 100 °C. The results show that, elevated curing temperatures improves the early age strength in the all cement mortars. Also, the results indicated that, the pozzolanic cement mortars gives higher compressive strength than the plain cement mortars, especially at curing temperatures above 35 °C. Therefore, slag pozzolanic cement mortars can be beneficially used in the hot conditions.

Artificial pozzolanic cement pastes containing burnt clay with and without silica fume

Pozzolanic cement blends were prepared by the partial substitution of ordinary Portland cement (OPC) with different percentages of burnt clay (BC), Libyan clay fired at 700 °C, of 10, 20, and 30%. The pastes were made using an initial water/solid ratio of 0.30 by mass of each cement blend and hydrated for 1, 3, 7, 28, and 90 days. The pozzolanic OPC–BC blend containing 30% BC was also admixed with 2.5 and 5% silica fume (SF) to improve the physicomechanical characteristics. The hardened pozzolanic cement pastes were subjected to compressive strength and hydration kinetics tests. The results of compressive strength indicated slightly higher values for the paste made of OPC–BC blend containing 10% BC The results of DSC and XRD studies indicated the formation and later the stabilization of calcium silicates hydrates (CSH) and calcium aluminosilicate hydrates (C3ASH4 and C2ASH8) as the main hydration products in addition to free calcium hydroxide (CH). Scanning electron microscopic (SEM) examination revealed that the pozzolanic cement pastes made of OPC–BC mixes possesses a denser structure than that of the neat OPC paste. Furthermore, the addition of SF resulted in a further densification of the microstructure of the hardened OPC–BC–SF pastes; this was reflected on the observed improvement in the compressive strength values at all ages of hydration.

Physicochemical, Microstructural and Thermal Characteristics of Some Artificial Pozzolanic Cement Pastes Containing Burnt Clay with and without Silica Fume

Physicochemical, Microstructural and Thermal Characteristics of Some Artificial Pozzolanic Cement Pastes Containing Burnt Clay with and without Silica Fume

Evaluation of calcium hydroxide contents in pozzolanic cement pastes by a chemical extraction method

The aim of the study is to investigate the calcium hydroxide (Ca(OH) 2) contents in pozzolanic cement pastes analyzed by the chemical extraction method and thermal analysis (DTA/TG). The second part of the study involves the carbonation of pozzolanic cement pastes and its influence on Ca(OH) 2 reduction. The Ca(OH) 2 contents in cement pastes after being subjected to accelerated carbonation were investigated by a chemical extraction method and compared to those values from DTA/TG analysis. The experimental results show that the chemical method reveals overall results comparable to those from DTA/TG analysis. However, in case of pastes containing high amounts of mineral admixtures or pastes subjected to carbonation which contain very low Ca(OH) 2, only the chemical method yields precise reliable results by showing the pseudo-negative contents.

Characterising cement–superplasticiser interaction using zeta potential measurements

The zeta potential generated at the interface between cement particle surfaces adsorbed with superplasticisers have been studied using electroacoustic technique, which is capable of measuring zeta potential at high concentrated suspensions. The study has been undertaken to examine the differences in the magnitude of the zeta potential for ordinary Portland cement (OPC) and Portland pozzolanic (fly ash) cement (PPC) pastes along with the differential impacts of different types of superplasticisers on both the varieties of cement pastes. In the latter context, the effects of three different types of superplasticisers namely Ligno Sulphonate (LS), Sulphonated Melamine Formaldehyde (SMF) and Sulphonated Naphthalene Formaldehyde (SNF) have been specifically studied. The results show that the cement pastes with PPC shows better dispersion when compared with the OPC. The paper also endeavors to unfold the relationship and significance of cement interaction with three different superplasticisers.

EFFECT OF CALCINATION TEMPERATURE OF KAOLINITE CLAY ON THE PROPERTIES OF PORTLAND CEMENT PASTES CONTAINING METAKAOLIN

Metakaolin (MK) is a highly reactive pozzolan produced by calcination of kaolinite clay at high temperatures. It has a high specific surface, which makes it very suitable as a cementing material in concrete. The utilization of area calcined clay, in the form of MK, as a pozzolanic material for mortar and concrete has received a considerable attention in recent years. This interest is part of the widely spread attention directed towards the utilization of wastes and industrial by-products in order to minimize Portland cement (PC) consumption, the manufacture of which being environmentally damaging. Another reason is that mortar and concrete, which contain pozzolanic materials, exhibit considerable enhancement in durability properties. In this investigation, the physico-chemical properties of artificial pozzolanic cement pastes containing MK produced by calcination of kaolinite clay at different temperatures (700, 800, 900, and 1000oC) were studied. PC was partially substituted for by 0, 5, 10, 15 and 20 % of MK by weight at different calcination temperatures. The characteristics of prepared mortars were investigated after curing in water for different periods (3, 7, 28 and 90 days) by determination of compressive strength and total porosity. The hydration kinetics was evaluated by determination of free lime contents. IR spectroscopic analysis was used to investigate the change in structure of mortars after curing. The change in morphology and microstructure of some hardened pastes were investigated by scanning electron microscopy (SEM).

Effect of calcium formate as an accelerator on the physicochemical and mechanical properties of pozzolanic cement pastes

The aim of the present work is to study the effect of calcium formate (CF) as an accelerator on the properties of pozzolanic cement pastes. Three types of cements were used in this investigation. These cements were OPC and pozzolanic cements containing 80 mass% OPC and 20 mass% silica fume (SF) or 20 mass% ground clay bricks (GCB). The dosages of CF were 0.00, 0.25, 0.50, and 0.75 mass% of cement. The compressive strength, total porosity, and hydration kinetics such as free lime and combined water contents were investigated. The results obtained in this study showed that the addition of CF shortens the initial and final setting times and increases the compressive strength and combined water content as well as gel/space ratio at all ages of hydration. On the other hand, it decreases the total porosity. CF activates the liberation of Ca(OH) 2 of OPC pastes. The free lime content of pozzolanic cement in the presence of CF increases up to 7 days, then decreases at the later ages of hydration.

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.

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

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.

Microstructure and hydration characteristics of artificial pozzolana-cement pastes containing burnt kaolinite clay

The reaction of pozzolana with the lime liberated during the hydration process of Portland cement modifies some properties of cement and resulting concrete. This study aimed to investigate experimentally the change occurring in the phase composition and microstructure of pozzolanic cement pastes containing activated kaolinite clay. The artificial pozzolana (burnt kaolinite clay) were thermally activated by firing at 850 °C for two hours. The ordinary Portland cement (OPC) was partially replaced by different amounts of activated kaolinite clay by weight. The changes in the electrical conductivity were reported during setting and hardening processes after gauging with water. The change occurring in the phase composition and microstructure of cement pastes were investigated by differential thermal analysis and scanning electron microscopy. The results of this investigation show that, the thermal activated kaolinite clay prolonged the initial and final setting times and reduced the porosity, it also improved the microstructure of the formed hydrates by recrystallization of hydrated calcium silicates (mainly as CSH-(I)) together with the formation of hexagonal calcium aluminate hydrate (mainly as C 4AH 13).

Pozzolanic cements

Natural and artificial pozzolanas have been used to obtain hydraulic binders for over a thousand years. Hardening of pozzolanic cement pastes can result from the reaction between pozzolana and the lime that is added to the mix as hydrated lime or is produced following hydration of portland cement silicates. The pozzolanic reaction does not alter cement clinker hydration; it complements and integrates the hydration process because it results in a lower portlandite content and an increase in calcium silicate hydrates. Besides reviewing the most recent investigations on pozzolana-containing cements, this paper shows that the behaviour of different types of pozzolana can be quite similar when they are blended and become hydrated along with portland cement clinker. Portland cement properties may undergo several qualitative modifications the extent of which substantially depends on the pozzolana/clinker ratio. So, a maximum is reached in pozzolanic cements. As in the case of pozzolanic cements, for which the current pozzolana content is about one third by weight of cement, the most outstanding variations induced in the behaviour of portland cement can be summarised as follows. Heat of hydration decreases whilst the rate of clinker hydration increases, paste porosity increases and permeability decreases, both portlandite content and Ca/Si ratio in C-S-H decrease and the C-S-H content increases. Chemical and physical properties of pozzolanic cements eventually affect engineering ones. Early strength of both pastes and concretes decreases while ultimate strength is often found to exceed that of the reference portland cement. If cements contain small amounts of very active pozzolana (silica fume, for example), both early and ultimate strengths may be higher than those of the substituted cement. Creep is found to increase definitely with increasing pozzolana content whereas shrinkage remains practically unaffected. Chemical and microstructural variations in the paste also influence resistance of concretes to environmental attacks. The low basicity and permeability resulting from the presence of pozzolana increase the concrete's resistance to lime leaching, sulphate and sea water attacks, and chloride penetration. Carbonation depth is practically unaffected. Pozzolana containing cements can help avoid expansion induced by alkali-silica reaction. Concrete resistance to freezing is not affected by the use of pozzolanic cement since it basically depends on the entrained air content. The results of a variety of studies introducing a comparison between pozzolana-containing cements and corresponding portland cements can be summarised as follows: cements with appreciable pozzolana contents perform better in the long term rather than at an early age. In most cases, however, the differences between the two types of cements are not so marked and as a consequence both cements are interchangeable especially for the most common building types.

Microstructure and Porosity of Metakaolin Blended Cements

AbstractFive compositions with 10% to 50% metakaolin for cement substitution were studied. The rate of hydration was studied from the compressive strength after up to 6 months of curing and from the hydrates formed (DTA-XRD). The metakaolin addition considerably reduced portlandite content in the hydrated cement and contributed to the formation of hydrated gehlenite which is not present in OPC paste. The microstructure study (SEM) shows that pozzolanic cement pastes were less crystallized than plain pastes. Mercury intrusion was used to measure porosity of hydrated cement pastes. The porosity with blended cements was higher than that with OPC, except for 10 and 20% metakaolin substitution. Evolution of the pore size distribution was studied: the pozzolanic pastes enhance small diameters.