Influence of calcined kaolin on mortar properties

The use of calcined clay, in the form of metakaolin (MK), as a pozzolanic material for mortar and concrete has received considerable attention in recent years. The present paper describes the results of a research project initiated to study the calcination of local kaolin at various temperatures (650–950 °C) and durations (2, 3 and 4 h) to produce MK with a high pozzolanic activity. The pozzolanic activity was assessed by 28-days compressive strength and hydration heat methods. The maximum identified activity was obtained at 850 °C for 3 h duration. An increase of both hydration heat and compressive strength was obtained when ordinary Portland cement was replaced by 10% MK. The use of ternary blended cement improves the early age and the long-term compressive strength. The durability was also enhanced as better acidic resistance was observed.     

Metakaolin,a solution for the precast industry to limit the clinker content in concrete: Mechanical aspects

The current trend to decrease the clinker content in cements through the use of mineral additions in order to limit CO₂ emissions into the atmosphere is of major concern for the precast industry as the resulting binders are generally not very reactive at early ages. Here, composed cements (clinker + slag) or combinations between clinker and mineral admixtures are studied with a view to investigating the compressive strength of cement-based materials at both early (1 day) and later (28 days) ages under steam curing conditions. Limestone and siliceous fillers, silica fume and four metakaolins differing in their production process and impurity content were investigated. Considering performance, economic and environmental criteria, results in the laboratory showed that metakaolin (MK) is a very promising solution at a clinker replacement rate of 12.5–25% by mass. Compressive strength was significantly increased (1-day age) or practically the same as for reference mortars incorporating cement only (28-day age). Thus, in comparison with a reference concrete containing no MK and for an identical granular skeleton, the combination clinker/MK was validated in the precast factory in full-scale trials for slip-forming (25% replacement) and self-compacting (17.5% replacement) concrete applications: compressive strength and porosity were not affected.     

Increasing mortar strength with the use of activated kaolin by-products from paper industry

Making use of industrial by-product or waste clay to partially replace cement in concrete has greatly contributed to sustainable development of environment. This study investigated the optimal activation condition for producing high reactivity metakaolin (MK) by using kaolin by-products (KB) from paper industry. Initially, the material properties of KB were analyzed in this study and the results indicated its great potential to be treated by calcination to be a very effective pozzolan. Afterwards, MK samples produced from different activation treatments of KB, including different calcining temperature, calcining duration, initial temperature rise rime and grinding particle size, were applied in mortar to determine their pozzolanic effect. Results indicated that the optimal activation condition for KB to high reactivity MK conversion is 2-h calcining duration at 750 °C and with 7 μm grinding particle size. Finally, compressive and flexural strengths of mortar samples produced by replacing cement with 0–25% MK content were tested and the results showed that 15% was the optimal cement replacement level of MK and the mortar so produced exhibited 20% improvement in compressive strength compared to control mortar.     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

Effect of metakaolin and foundry sand on the near surface characteristics of concrete

This paper deals with the effect of foundry sand (FS) and metakaolin (MK) on the near surface characteristics of concrete. A control concrete having cement content 450 kg/m³ and w/c of 0.45 was designed. Cement was replaced with three percentages (5%, 10%, and 15%) of metakaolin weight, and fine aggregates were replaced with 20% foundry sand. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days.Test results indicated that with the increase in MK content from 5% to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics. Inclusion of foundry sand resulted in reduction in compressive strength. This aspect cements the findings that addition of FS causes permeability of concrete to increase causing in an increase in sorptivity and water absorption of concrete.     

Metakaolin sand–blended-cement pastes: Rheology,hydration process and mechanical properties

In the present work, the use of three Slovak poor metakaolin sands with different metakaolin content (36.0% (MK-1), 31.5 (MK-2) and 40.0% (MK-3)) and specific surface has been deeply studied as mineral addition for Portland cement. The percentage of metakaolin sands in the blended cements was 10%, 20% and 40%.The pozzolanic tests confirm that the three metakaolin sands show a high pozzolanic activity, comparable to a commercial metakaolin and silica fume. With respect to the rheological behaviour, metakaolin sand–blended-cement pastes fit to Herchel–Bulkley model and their yield stress increases as the metakaolin content increases. MK-3 sand with the highest pozzolanic activity and highest specific surface induces the highest increase of the yield stress.From the calorimetric results it is concluded that the addition of MK-1 and MK-2 sands to Portland cement induces a delay up to 2 h of the precipitation of the main hydration products in the blended-cement pastes and decreases the maximum heat evolution rate. On the contrary, the incorporation of 40% of MK-3 sand shortens 6 h its apparition and increases significantly the maximum heat evolution rate. Additionally, the presence of the metakaolin sands reduces the heat released during the hydration process with respect to non-blended-cement pastes.The incorporation of metakaolin sand induces a decrease of the mechanical strength, being the decrease higher as the metakaolin sand content increases although they also produce a refinement in the pore structure and a decrease of the permeability.     

Effects of crushed glass cullet sizes,casting methods and pozzolanic materials on ASR of concrete blocks

The aim of this study is to investigate the influence of using different particle sizes of recycled glass, casting methods and pozzolanic materials in reducing the expansion due to alkali-silica reaction (ASR) of concrete blocks prepared with the use of crushed glass as fine aggregate. In this work, 25 × 25 × 285 mm mortar bar specimens were prepared using conventional wet-mixed and dry-mixed methods. Except for the control mortar bar, all the specimens were prepared by completely replacing river sand with different particle sizes of recycled glass. In addition, the influence of fly ash (PFA) and metakaolin (MK) content on the reduction of ASR expansion was also investigated. The flexural strength of the mortar bar specimens before and after they had been exposed to 1N NaOH solution was determined to complement the results of ASR expansion test. SEM was performed to examine the microstructure as well as nature of the cement binder-glass interfacial zone. The results reveal that ASR expansion reduced with reducing particle size of glass used. For the same given mix proportion, the dry-mixed method resulted in 44% less expansion when compared with the wet-mixed method. Both PFA and MK were demonstrated to be able to significantly reduce ASR expansion of the concrete glass blocks.     

Hydration heat kinetics of concrete with silica fume

The objective of this study was to evaluate the influence of silica fume on the hydration heat of concrete. Portland cement was replaced by silica fume in amounts from 10 % to 30 % by mass in concrete with w/(c+sf) ratios varying between 0.25 and 0.45. A superplasticizer was used to maintain a fluid consistency. The heat of hydration was monitored continuously by a semi-adiabatic calorimetric method for 10 days at 20 °C. The calorimetric study indicated that the hydration was modified by the presence of silica fume. In the early stages, the silica fume showed a high activity and accelerated the hydration rate as compared to that of the reference concrete. The fine silica fume particled provided nucleation sites for hydrates growth. Then the pozzolanic activity took over and increased both strength and the hydration heat. A substitution of Portland cement by 10% with silica fume produced greater strength and cumulative heat of hydration as compared to that of the reference concrete.     

Compressive strength and hydration with age of cement pastes containing dune sand powder

This experimental work has focused on studying the possibility of using dune sand powder (DSP) as a part mass addition to Portland cement. Studying the effect of addition dune sand powder on development of compressive strength and hydration with age of cement pastes as a function of water/binder ratio, was varied, on the one hand, the percentage of the dune sand powder (physico-chemical and chemical effect) and on the other, the fineness of dune sand powder (physical effect). In order to understand better the chemical effect (pozzolanic effect) of dune sand powder in cement pastes, we followed the mixtures hydration (50% pure lime + 50% DSP) by X-ray diffraction. These mixtures pastes present a hydraulic setting which is due to the formation of a C–S–H phase (calcium silicate hydrate). The latter is semi-crystallized. This study is a simplified approach to that of the mixtures (80% ordinary Portland cement + 20% DSP), in which the main reaction is the fixing of the lime coming from the cement hydration in the presence of the dune sand powder (pozzolanic reaction), to form calcium silicate hydrate C–S–H semi-crystallized of second generation. The results proved that up to 20% of dune sand powder as Portland cement replacement could be used with a fineness of 4000 cm²/g without affecting adversely the compressive strength. The dune sand powder, despite its crystalline nature, presents a partial pozzolanic reactivity.     

Effect of rice husk ash on the strength and durability characteristics of concrete

This work investigates the effects of adding residual rice husk ash (RHA) from South Vietnam, generated when burning rice husk pellets in the boiler, to cement. To improve pozzolanic reactivity, RHA was ground for 1 h. The non-ground RHA and ground RHA were used to test strength activity index according to ASTM C311. The properties of the concrete were investigated, including compressive strength, concrete electrical resistivity, and ultrasonic pulse velocity. Results show that the non-ground RHA can be applied as a pozzolanic material. Decreasing the non-ground RHA average particle size provides a positive effect on the compressive strength of mortar. Compressive strength of cylindrical concrete in the 47–66 MPa range was obtained in this study. The results also indicate that up to 20% of ground RHA could be advantageously blended with cement without adversely affecting the strength and durability properties of concrete.     

Filler effect and pozzolanic reaction of ground palm oil fuel ash

This research examines the compressive strength of mortar and how the filler effect and pozzolanic reaction of ground palm oil fuel ash (POFA) contribute to this strength. POFA and river sand were ground to three different particle sizes and used to replace Type I Portland cement at 10–40% by weight of binder to cast the mortar. The compressive strengths of ground POFA and ground river sand mortars were determined at various ages between 7 and 90 days. The results showed that the compressive strength of mortar due to the filler effect of ground river sand was nearly constant during the 7–90 day period for a specified replacement rate of cement. However, the compressive strength of mortar due to the filler effect tended to increase slightly with increased cement replacement. The pozzolanic reaction of ground POFA increased with increasing particle fineness of ground POFA, replacement rate of cement, and age of the mortar. The compressive strength contribution from the pozzolanic reaction of ground POFA was much more pronounced than the contribution from the filler effect when the smallest sizes of both materials were considered.     

Effects of curing regimes and cement fineness on the compressive strength of ordinary Portland cement mortars

Curing techniques and curing duration have crucial effects on the strength and other mechanical properties of mortars. Proper curing can protect against moisture loss from fresh mixes. The objective of this experimental work is to examine the compressive strength of ordinary Portland cement mortars (OMs) under various curing regimes and cement fineness. Six different curing methods including water, air, water heated, oven heated, air–water, and water–air were applied to the specimens and also six groups of mortars were used. The results showed that the highest and lowest compressive strengths are attributed to the specimens of OPC mortar water cured using grounded OPC for duration of 6 h (OM–G6–wc) and OPC mortar air cured under room temperature with oven heated after demoulding of the specimens at 60 °C for duration of 20 h (OM–OH–ac), respectively. The maximum levels obtained of compressive strengths at 7, 28, and 90 days are 57.5, 70.3, and 76.0 MPa, respectively.     

Effect of elevated temperature on physico-mechanical properties of blended cement concrete

Pozzolanas are readily available for use in concrete in the local markets for strength and/or durability enhancement. Although safety and security against disasters are not new, they still presuming a challenge. For instance, the fire resistive properties of concrete are of prime interest.Through this work, the effect of different kinds of pozzolana on the fire resistive properties of concrete was studied. Four types of pozzolana were incorporated into the concrete mixtures, i.e. metakaolin (MK), silica fume (SF), fly ash (FA), and ground granulated blast furnace slag (GGBS). Each of the employed pozzolana was used in two ratios: 10% and 20%, either in the form of cement replacement or as an addition without affecting the cement content. A total of 17 mixes were cast.For all mixtures, compressive strength is evaluated after 28 days of water curing. The mixtures’ compressive strengths were also evaluated after exposure to elevated temperatures: 200 °C, 400 °C, 600 °C, and 800 °C. The residual compressive strengths after heat exposure are evaluated. The formed cementitious phases after incorporation of pozzolana and the heat-induced transformations are investigated via the X-ray diffraction technique (XRD).Test results demonstrate the impact of each type of the employed pozzolana on the heat resistive properties of concrete in addition to their influence on the strength development of the investigated mixes. Therefore, a decision could be made regarding optimizing the benefits specific to each type of pozzolana and their employment method.     

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.     

Physical and mechanical properties of durable sisal fiber–cement composites

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.     

Metakaolin concrete at a low water to binder ratio

This paper investigates the performance of concrete containing metakaolin (MK) at a low water to binder ratio of 0.3. Portland cement (PC) was partially replaced with 0–20% MK. Testing included, compressive strength, ultrasonic pulse velocity (V), dynamic modulus of elasticity (E_d) and length change. Specimens were either cured in water or in air at 20 °C. The results indicate that the performance of MK concrete at low water to binder ratio is not different from that at higher water to binder ratios reported in a previous investigation. The maximum contribution of MK to strength occurs at 14 days of curing in that the relative strength of MK concrete shows a maximum value at that curing time as found in a previous investigation. The optimum replacement level of cement with MK is about 15%. Linear relationship exists between V and E_d for air cured and water cured specimens. A systematic increase in MK content of up to at least 20% leads to a decrease in shrinkage and an increase in expansion after 56 days of curing. Correlation between the various properties is also conducted.     

Properties of blended cements with thermally activated kaolin

Kaolin, one of the materials of major importance for the ceramic and paper industry, is also used in the construction industry as a raw material for the production of white cement clinker and, in the form of metakaolin, as an artificial pozzolanic additive for concrete. Metakaolin is a vital component of high-performance and architectural concrete; however, its application in regular concrete is very limited due to relatively high production costs. This report evaluates the performance of a low-cost metakaolin-based additive called thermally activated kaolin (TAK), in cement. Due to its pozzolanic properties and the densification of cement matrix, the application of TAK provides a 15% improvement of the compressive strength. It was shown that TAK of optimal quality can be manufactured by the thermal treatment of raw kaolin with 74% of kaolinite at 750 °C without the intermediate beneficiation stage. The application of a developed approach can significantly reduce production expenditures and make the application of such an additive feasible even in regular-grade cement and concrete.     

Use of palm oil fuel ash as a supplementary cementitious material for producing high-strength concrete

The objective of this study is to investigate the use of ground palm oil fuel ash with high fineness (GPA) as a pozzolanic material to produce high-strength concrete. Samples were made by replacing Type I Portland cement with various proportions of GPA. Properties such as the compressive strength, drying shrinkage, water permeability, and sulfate resistance, were then investigated. After aging for 28 days, the compressive strengths of these concrete samples were found to be in the range of 59.5–64.3 MPa. At 90-day the compressive strength of concrete containing GPA 20% was as high as 70 MPa. The drying shrinkage and water permeability were lower than those of high-strength concrete made from Type I Portland cement. When the concrete samples were immersed in a 10% MgSO₄ solution for 180 days, the sulfate resistance in terms of the expansion and loss of compressive strength was improved. The results indicated that GPA is a reactive pozzolanic material and can be used as a supplementary cementitious material for producing high-strength concrete.     

Influence of pozzolan from various by-product materials on mechanical properties of high-strength concrete

This paper presents experimentally investigated the effects of pozzolan made from various by-product materials on mechanical properties of high-strength concrete. Ground pulverized coal combustion fly ash (FA), ground fluidized bed combustion fly ash (FB), ground rice husk–bark ash (RHBA), and ground palm oil fuel ash (POFA) having median particle sizes less than 11 μm were used to partially replace Portland cement type I to cast high-strength concrete. The results suggest that concretes containing FA, FB, RHBA, and POFA can be used as pozzolanic materials in making high-strength concrete with 28-day compressive strengths higher than 80 MPa. After 7 days of curing, the concretes containing 10–40% FA or FB and 10–30% RHBA or POFA exhibited higher compressive strengths than that of the control concrete (CT). The use of FA, FB, RHBA, and POFA to partially replace Portland cement type I has no significant effect on the splitting tensile strength and modulus of elasticity as compared to control concrete or silica fume concretes. This results suggest that the by-products from industries can be used to substitute Portland cement to produce high-strength concrete without alteration the mechanical properties of concrete.     

Mechanical properties of normal and high strength concretes subjected to high temperatures and using image analysis to detect bond deteriorations

The effect of high temperatures, up to 250 °C, on mechanical properties of normal and high strength concretes with and without silica fume was investigated, and image analysis was performed on split concrete surfaces to see the change in bond strength between aggregate and mortar. Specimens were heated up to elevated temperatures (50, 100, 150, 200, 250 °C) without loading and then the residual compressive and splitting tensile strength, as well as the static modulus of elasticity of the specimens were determined. For normal strength concrete residual mechanical properties started to decrease at 100 °C, while using silica fume reduced the losses at high temperatures. In terms of percent residual properties, high strength concrete specimens performed better than normal strength concrete specimens for all heating cycles. Image analysis studies on the split surfaces have been utilized to investigate the effect of high temperatures on the bond strength between aggregate and mortar. Image analysis results showed that reduced water–cement ratio and the use of silica fume improved the bond strength at room temperature, and created more stable bonding at elevated temperatures up to 250 °C.