Extending blending proportions of ordinary Portland cement and calcium sulfoaluminate cement blends: Its effects on setting,workability, and strength development

This study extended blending proportion range of ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement blends, and investigated effects of proportions on setting time, workability, and strength development of OPC-CSA blend-based mixtures. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were conducted to help understand the performance of OPC-CSA blend-based mixtures. The setting time of the OPC-CSA blends was extended, and the workability was improved with increase of OPC content. Although the early-age strength decreased with increase of OPC content, the strength development was still very fast when the OPC content was lower than 60% due to the rapid formation and accumulation of ettringite. At 2 h, the OPC-CSA blend-based mortars with OPC contents of 0%, 20%, 40%, and 60% achieved the unconfined compressive strength (UCS) of 17.5, 13.9, 9.6, and 5.0 MPa, respectively. The OPC content had a negligible influence on long-term strength. At 90 d, the average UCS of the OPC-CSA blend-based mortars was 39.2 ± 1.7 MPa.     

A study on the hydration rate of natural zeolite blended cement pastes

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O_3. It is widely used in the cement industry in China as a cement blending material. Like other pozzolanic materials such as silica fume and fly ash, zeolite contributes to concrete strength mainly through the pozzolanic reaction with Ca(OH)₂, Thus, the pozzolanic reactivity of this type of material in comparison with other pozzolans is of much interest. This paper presents experimental results on the compressive strength, degree of pozzolanic reaction, and porosity of zeolite modified cement pastes. These results are compared with those obtained from similar blended cement pastes prepared with silica fume and fly ash replacements. Based on the experimental results, it can be concluded that natural zeolite is a pozzolanic material, with a reactivity between that of silica fume and fly ash. Generally, in blended cement pastes with a lower water-to-cementitious materials ratio, the natural zeolite contributes more to the strength of the pastes. But in the pastes with a higher water to cementitious ratio and a lower cement replacement level it undergoes a higher degree of reaction.     

Pozzolanic activity of Hwangtoh clay

Hwangtoh is a clay that has long been used as a traditional Korean building material. In these days, Hwangtoh is often used for plastering and flooring in newly constructed buildings to minimize sick building syndrome. In such applications, it is useful to determine whether the clay has pozzolanic properties. In this research, the pozzolanic activity of Hwangtoh clay was indicated by a reduction in calcium hydroxide and an increase in compressive strength in mortars, in which 20% of the Portland cement was replaced by the clay. The thermally activated Hwangtoh clay showed clear pozzolanic activity at 14 and 28 days, and the as-received clay showed some evidence of pozzolanic activity as well. The compressive strength provided by the activated clay was less than that provided by a synthetic mixture of metakaolin and quartzite, but still greater than that provided by the as-received Hwangtoh. The strength development may be improved further by removing the quartzite from the Hwangtoh clay.     

Metallurgical slag as a component in blended cement

Metallurgical slags (granulated and air-cooled), are disposed as waste from the ferro-manganese and ferro-manganese–silicon alloys manufacturing plants. They find little use unlike blast furnace slags from steel plants. Investigations were carried out to explore the possibility of using high MnO and low MnO metallurgical slags on samples obtained from an alloy plant in India. Low MnO granulated slag was used in making blended slag cement with ordinary Portland cement (OPC). Addition of slag lowered the compressive strength of the blended cement as compared to that of OPC used. However, the composition of a 50:50 blend, ground to 3000 cm²/g (Blaine), was found to conform to IS 455:1989 for Portland slag cements and also to IS 269:1989, 33 grade OPC, with respect to standard consistency, setting times, soundness and compressive strength (22 MPa at 7 days and 33 MPa at 28 days) tests carried out as per IS 4031:1988. X-Ray diffraction analysis showed that low MnO granulated slag was non-crystalline, whereas the air-cooled slags were crystalline containing mainly quartz, MnO and Mn₂O₃. Chemical analysis showed that the slag samples were low in CaO and Fe₂O₃ contents and high in SiO₂, Al₂O₃, MnO, MgO, Na₂O and K₂O, thus indicating pozzolanic reactions contributing to a great extent in the strength development of blended slag cement compositions studied. High MnO (>15%) and MgO (>8%) containing slags were considered unsuitable for blended cements because of their deleterious effects. Air-cooled lumpy slag was evaluated for use as aggregates in concrete. All the tests were carried out as per IS 2386:1963, methods of test for aggregate for concrete and to conform to IS 383:1990, coarse and fine aggregates from natural resources. The material passed all the tests viz. crushing strength, impact value, abrasion, alkali aggregate soundness, except for deleterious materials content. This slag could be used, with slight modification, for non-structural concrete. The results of the investigations provide a direction for profitable plans for making blended slag cements.     

Potential use of spent mushroom compost ash as an activator for pulverised fuel ash

The utilization of pulverised fuel ash (PFA) as a replacement material for Portland cement has resulted in improved concrete properties. However, the pozzolanic activity of PFA is slow, resulting in poor strength development of PFA concrete at early ages. To overcome this problem many researchers have investigated methods of activating (mechanically, thermally and chemically) the pozzolanic reactivity of PFA. This paper assesses the potential use of spent mushroom compost ash (SMCA) as a chemical activator for PFA blended cement systems.When added to the PFA/OPC paste mix SMCA had the effect of improving early strength development. X-ray diffraction results showed that, in the mix which contained 20% SMCA, ettringite formation was improved at both 7 and 28 days, whereas thermogravimetric analysis identified depletion of calcium hydroxide levels at both 3 and 7 days for the same sample pastes. It is therefore considered that the increased strength development in SMCA mixes is a result of the presence of large quantities of sulfates in SMCA, which, when hydrated, has activated the glassy phases present in PFA to form ettringite, as well as possibly accelerating the pozzolanic activity.     

在水热作用下废弃水泥基材料的再生研究

对水热作用下废弃水泥基材料的再生进行了研究.测试再生废弃水泥基材料的抗压强度、表观密度和吸水率等随氢氧化钙掺量的变化.结果表明,在废弃水泥净浆中掺加氢氧化钙对抗压强度增加不明显;在废弃水泥胶砂中当氢氧化钙掺量为15%时试样的抗压强度最高;在废弃混凝土中当氢氧化钙掺量为10%时试样的抗压强度最高.利用这种再生方法,可以充分利用废弃水泥基材料中的剩余胶凝材料和硅质材料.     

Effect of nonpozzolanic and pozzolanic mineral admixtures on the hydration behavior of ordinary Portland cement

The effects of nonpozzolanic (marble dust) and pozzolanic (rice husk ash) mineral admixtures on the hydration behavior and mechanical properties of ordinary Portland cement (OPC) have been investigated. The blending of both marble dust (20-60%) and rice husk ash (10-30%) in OPC accelerate the setting as compared to control (OPC). Marble dust addition decreases the strength of OPC and the maximum strength of 54.5 MPa has been achieved on 28 days of curing with 20% of marble dust (CM20). Addition of rice husk ash increases the strength and maximum strength of 65.9 MPa has been observed with 20% of RHA (CR20) blended cement. The formation of various crystalline phases and their effects on hydration behavior of mineral admixtures blended cement were examined by X-ray diffraction (XRD). The changes in microstructure of the hydrated samples were also studied using scanning electron microscope (SEM).     

The pozzolanic properties of paper sludge waste

The use of paper de-inking sludge in pozzolanic material manufacture permits a disposable residue to be included in the cycle of the materials. A study on the reuse of paper de-inking sludge, undertaken in Spain, shows its potential as raw material for yielding a product with pozzolanic activity.

This study establishes that an optimal condition for transforming paper de-inking sludge into a pozzolanic addition is achieved at 700 °C maintained for 2 h. Under these conditions, the organic matter disappears and the calcined sludge becomes active by transforming kaolinite into metakaolinite. The calcined product exhibits high pozzolanic activity.

The present paper also analyses mechanical, physical and chemical properties of a blended cement containing 90% (in mass) standard Portland cement (CEM I-52,5N) and 10% of the pozzolanic addition obtained from controlled calcination of paper de-inking sludge (for 2 h at 700 °C). When the blended cement is compared with a cement containing 100% standard Portland cement, the following conclusions can be mentioned: a significant gain in compressive strength from 7 days on, a sooner initial setting time, as well as a reduction in SO₃ percentage. In any case, the new blended cement complies with requirements set out in Spanish/European standard UNE EN 197-1-Part 1.     

Characteristics of cement mortar with nano-SiO2 particles

The properties of cement mortars with nano-SiO₂ were experimentally studied. The amorphous or glassy silica, which is the major component of a pozzolan, reacts with calcium hydroxide formed from calcium silicate hydration. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. Therefore, it is plausible to add nano-SiO₂ particles in order to make high-performance concrete. The experimental results show that the compressive strengths of mortars with nano-SiO₂ particles were all higher than those of mortars containing silica fume at 7 and 28 days. It is demonstrated that the nano-particles are more valuable in enhancing strength than silica fume. In addition, the continuous hydration progress was monitored by scanning electron micrograph (SEM) observation, by examining the residual quantity of Ca(OH)₂ and the rate of heat evolution. The results of these examinations indicate that nano-scale SiO₂ behaves not only as a filler to improve microstructure, but also as an activator to promote pozzolanic reaction.     

Physico-chemical,morphological and thermal analysis for the combined pozzolanic activities of minerals additives

The research was aimed to evaluate the physico-chemical, morphological and thermal analysis of combined pozzolanic activities of minerals additives. Fly ash and ground granulated blast furnace slag were added, separately and collectively, as mineral replacement in ordinary Portland cement. Tests carried out on specimens cured at different ages were: compressive strength, ultrasonic pulse velocity, X-ray diffraction (XRD) analysis, scanning electron microscopic (SEM) studies, differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA), etc. The results indicated that the compressive strength and ultrasonic pulse velocity development rate of concrete specimens were significantly influenced by the addition of mineral additives. SEM data showed that the fly ash particles were more embedded and surrounded by slag. XRD analysis and DTA/TGA investigation have revealed different reaction kinetics of paste. The peak intensity of calcium hydroxide was significantly retarded by the addition of fly ash and slag, especially in combination, attributed to the dilution effect and calcium hydroxide consumption by pozzolanic reaction.     

Effect of different mixing ratios of polystyrene pre-puff beads and cement on the mechanical behaviour of lightweight fill

A laboratory study on the formation of a lightweight fill material by blending soil with polystyrene pre-puff (PSPP) beads and other binders such as cement is presented in this paper. The effects of different compositions and different ratios between PSPP beads and soil, cement and soil, water and soil on the density, unconfined compressive strength and deformation of the lightweight fill formed are studied. It is observed that the density of the lightweight fill can be effectively controlled by the amount of PSPP beads used in making the fill. With the inclusion of merely 2–6% of PSPP beads (to soil by weight), the density of the lightweight fill formed can be reduced to 700–1100 kg/m³. The shear strength and stiffness of the lightweight fill can be controlled by adjusting the amount of cement used. The unconfined compressive strength of the lightweight fill increases considerably if a cement to soil ratio of 10–15% is used. Compared with the expanded polystyrene (EPS) block geofoam, the PSPP beads mixed lightweight fill has a higher density, but higher shear strength and higher stiffness too. It can be used as a substitute of EPS blocks when irregular shaped volumes are to be filled or when stronger fill materials are required.     

Strength and water permeability of concrete containing palm oil fuel ash and rice husk–bark ash

In this paper, palm oil fuel ash and rice husk–bark ash, which are by-products from electricity generating power plants and disposed as wastes in landfills, were used as a partial cement replacement. They were ground and incorporated into concrete at the levels of 20%, 40% and 55% by weight of binder. Compressive strength and water permeability of concretes containing ground palm oil fuel ash (GPOA) and ground rice husk–bark ash (GRBA) were investigated. From the tests, the replacement of Portland cement by both materials resulted in the higher water demand in concrete mixtures as compared to ordinary Portland cement (OPC) concrete with compatible workability. The compressive strengths of concretes containing 20% of GPOA and GRBA were as high as that of OPC concrete and were reduced as the increase in the replacement ratios. Although the compressive strengths of concrete with the replacement of GPOA or GRBA up to 40% were lower than OPC concrete, their water permeabilities were still lower than that of OPC concrete. These results indicate that both of GPOA and GRBA can be applied as new pozzolanic materials to concrete with an acceptable strength as well as permeability.     

Utilization of separator bag filter dust for high early strength cement production

This paper presents the feasibility of incorporating ultra-fine particles collected in the separator bag filter during the process of manufacturing cement (SBFC) as an substitution material for cement. Approximately 2.5% of SBFC is produced during OPC manufacturing process. Also, the average size of SBFC particles is about 5 μm, the average size of OPC particles is about 14 μm. This method does not require additional processes needed in the existing processes to manufacture high early strength cement such as modifying mineral components and adjusting the firing temperature. Moreover, it can also solve the issue of efficiency decrease resulted from the increase of the grinding time applied in the existing process of manufacturing microcement. In order to investigate the characteristic properties of this cement mixture, cement blends have been produced by using different amounts of SBFC. While the blaine value of 100% SBFC was significantly higher (6953 cm²/g) than that of Ordinary Portland Cement (OPC), its chemical composition showed no significant difference. Cement paste, mortar mixtures have been prepared by using cement blends incorporating 0, 50 and 100% SBFC by weight. Flowability, setting time and compressive strength tests has been performed. Test results showed that substitution of SBFC negatively affect the flowability of cement paste and mortar mixtures. Moreover, setting times shortened, compressive and flexural strength values increased by the substitution of SBFC. Finally, microstructure analysis of cement paste samples showed that incorporation of SBFC reduced the internal porosity by 9% as determined by the proposed method. The internal porosity of paste was measured by mercury intrusion porosimetry (MIP). The compressive strength and bending strength of mortar were higher in the order of 100, 50 and 0% SBFC mixed.     

Properties of cement—rice husk mixture

The properties of lightweight mortar using rice husk can benefit from pozzolanic reaction and from organic fibre reinforcement. The effect of curing and storage on 40×40×160 mm³ OPC rice husk mortar specimens is described. Two conditions are studied; one-year storage at 50% RH and at 95% RH. The final specimen properties were characterised by density, strength, SEM, EDS and XRD. It is concluded that at high humidity storage, pozzolanic reaction is well developed but husk fibres deteriorate. The mortar stored at 50% RH has a lower compressive strength and higher flexural strength, indicating inferior pozzolanic reaction and active fibre reinforcement.     

Production of high strength concrete by use of industrial by-products

Blast furnace slag aggregates (BFSA) were used to produce high-strength concretes (HSC). These concretes were made with total cementitious material content of 460–610 kg/m³. Different water/cement ratios (0.30, 0.35, 0.40, 0.45 and 0.50) were used to carry out 7- and 28-day compressive strength and other properties. Silica fume and a superplasticizer were used to improve BFSA concretes. Slump was kept constant throughout this study. Ten percent silica fume was added as a replacement for ordinary portland cement (OPC) in order to obtain HSC. The silica fume was used as highly effective micro-filler and pozzolanic admixture. Superplasticizer at dosages of 2%, 1.5%, 1%, 0.5% and 0% by OPC weight for 0.30, 0.35, 0.40, 0.45 and 0.50 w/c ratios, respectively, were adopted. Results showed that compressive strength of BFSA concretes were approximately 60–80% higher than traditional (control) concretes for different w/c ratios. These concretes also had low absorption and high splitting tensile strength values. It is concluded that BFSA, in combination with other supplementary cementitious materials, can be utilized in making high strength concretes.     

Availability of tuffs from northeast of Turkey as natural pozzolan on cement, some chemical and mechanical relationships

At Northeast of Turkey, it is possible to find plenty of volcanic origin rocks and rich natural pozzolan beds. In this study, the pozzolanic activities of six types of different tuff samples taken from Trabzon and Bayburt regions (Northeast of Turkey) were examined according to the related standard and it was determined that the compressive strengths were varying between 6.7–11.0 MPa. In addition, the chemical compositions of these samples, except one, were consistent with the related standard. On the other hand, the results obtained from these studies were that increase in the proportion of SiO₂ in the pozzolan increases the pozzolanic activity.     

Study on the pozzolanic properties of a natural Cuban zeolitic rock by conductometric method: Kinetic parameters

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O₃. These materials have been used in the cement industry as a supplementary cementing material. Like other pozzolanic materials the zeolite contributes to improve the mortar and concrete performances mainly through the pozzolanic reaction with calcium hydroxide (CH). The pozzolanic reactivity of this type of material in comparison with other pozzolans is of great interest.The current paper presents a study about the pozzolanic activity of a natural Cuban zeolitic rock. The pozzolanic activity in a zeolitic material/CH solution is investigated by means of electrical conductivity measurements and latter on the kinetic parameters are quantified by applying a kinetic–diffusive model to process. The kinetic parameters that characterize the process (in particular the reaction rate constant) were determined in the fitting process of the model. The index of pozzolanic activity evaluated according to the obtained values of the reaction rate constant permits to characterize the pozzolanic activity of these materials in a rigorous way.The results show that this Cuban zeolitic rock is a natural material with high pozzolanic activity. Also, these results allow corroborating the direct influence of the fineness of zeolitic material on the pozzolanic and mechanical properties.     

Effect of palm oil fuel ash fineness on the microstructure of blended cement paste

This paper presents the effect of palm oil fuel ash fineness on the microstructure of blended cement paste. Palm oil fuel ash (POFA) was ground to two different finenesses. Coarse and high fineness palm oil fuel ash, with median particle sizes of 15.6 and 2.1 μm, respectively, were used to replace ordinary Portland cement (OPC) at 0%, 20% and 40% by binder weight. A water to binder (W/B) ratio of 0.35 was used for all blended cement pastes. The amorphous ground palm oil fuel ash was characterized by the Rietveld method. The compressive strength, thermogravimetric analysis and pore size distribution of the blended cement pastes were investigated. The test results indicate that the ground palm oil fuel ash was an amorphous silica material. The compressive strengths of the blended cement pastes containing coarse POFA were as high as that of OPC cement paste. Blended cement paste with high fineness POFA had a higher compressive strength than that with coarse POFA. The blended cement pastes containing 20% of POFA with high fineness had the lowest total porosity. The Ca(OH)₂ contents of blended cement paste containing POFA decreased with increasing replacement of POFA and were lower than those of the OPC cement paste. In addition, the POFA fineness had an effect on the reduction rate of Ca(OH)₂. Furthermore, the critical pore size and average pore size of blended cement paste containing POFA were lower than those of the OPC cement paste. The incorporation of high fineness POFA decreased the critical pore size and the average pore size of blended cement paste as compared to that with coarse POFA.     

Effect of calcium lactate on compressive strength and self-healing of cracks in microbial concrete

This paper presents the effect on compressive strength and self-healing capability of bacterial concrete with the addition of calcium lactate. Compared to normal concrete, bacterial concrete possesses higher durability and engineering concrete properties. The production of calcium carbonate in bacterial concrete is limited to the calcium content in cement. Hence calcium lactate is externally added to be an additional source of calcium in the concrete. The influence of this addition on compressive strength, self-healing capability of cracks is highlighted in this study. The bacterium used in the study is bacillus subtilis and was added to both spore powder form and culture form to the concrete. Bacillus subtilis spore powder of 2 million cfu/g concentration with 0.5% cement was mixed to concrete. Calcium lactates with concentrations of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% of cement, was added to the concrete mixes to test the effect on properties of concrete. In other samples, cultured bacillus subtilis with a concentration of 1×10⁵ cells/mL was mixed with concrete, to study the effect of bacteria in the cultured form on the properties of concrete. Cubes of 100 mm×100 mm×100 mm were used for the study. These cubes were tested after a curing period of 7, 14, and 28 d. A maximum of 12% increase in compressive strength was observed with the addition of 0.5% of calcium lactate in concrete. Scanning electron microscope and energy dispersive X-ray spectroscopy examination showed the formation of ettringite in pores; calcium silicate hydrates and calcite which made the concrete denser. A statistical technique was applied to analyze the experimental data of the compressive strengths of cementations materials. Response surface methodology was adopted for optimizing the experimental data. The regression equation was yielded by the application of response surface methodology relating response variables to input parameters. This method aids in predicting the experimental results accurately with an acceptable range of error. Findings of this investigation indicated the influence of added calcium lactate in bio-concrete which is quite impressive for improving the compressive strength and self-healing properties of concrete.     

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.