Compressive strength of ash-based geopolymers at early ages designed by Taguchi method

In the present work, compressive strength of ash-based geopolymers has been designed by Taguchi method at 2 and 7 days of water curing. Three factors including oven curing temperature (at 3 levels of 25, 70, and 90 °C), oven curing time (at 3 levels of 2, 4, and 8 h) and sodium hydroxide (NaOH) concentration (at 3 levels of 5, 8, and 12 M) were considered. By utilizing L9 Taguchi array, 9 series of experiments were conducted on the prepared specimens. The aluminosilicate source was a mixture of fly ash and rice husk ash while the alkali activating was done by a mixture of NaOH and sodium silicate solution. The obtained results were evaluated by analysis of variance (ANOVA) method to determine the optimum level of each factor. In all produced specimens, the optimum level of oven curing temperature was always 90 °C to achieve the highest compressive strength. Furthermore, the optimum strength was obtained by applying light and middle concentration of NaOH in approximately all specimens. Finally, the oven curing time was not an important factor to determine the compressive strength. To validate the accuracy of the optimum conditions suggested by ANOVA, compressive specimens were made and tested in accordance to the optimum conditions for each of 2 and 7 days water curing regimes. The compressive strength acquired from this situation was higher than those of proposed in initial 9 series of experiments for each of 2 and 7 days water curing regimes.     

Compressive strength of high strength class C fly ash-based geopolymers with reactive granulated blast furnace slag aggregates designed by Taguchi method

Compressive strength of geopolymeric specimens produced by class C fly ash and granulated blast furnace slag aggregates has been studied. Four different independent factors comprising of aggregate content, sodium hydroxide concentration, curing time and curing temperature were considered as the variables. To attain the maximum possible accurate responses by means of the smallest amount of examinations, Taguchi design of experiment method was followed. By taking into account three levels for each factor, 9 series of experiments were conducted on the specimens at 2 and 7 days of water curing regime. For both considered regimes, a specimen with 30 weight percent of aggregate and sodium hydroxide concentration of 12 M cured at 90 °C for 16 h had the highest compressive strength. On account of reactivity between aggregates and the fly ash, the compressive strength was reached to 69.3 ± 5.3 MPa and 76.2 ± 3.6 MPa at 2 and 7 days of water curing, respectively. Fracture surface of specimens with the highest and the lowest strengths as well as effect of each considered factor on the compressive strength of the specimens were studied.     

Sintering effect on cement bonded sewage sludge ash

Through foaming reaction, hydration reaction and pozzolanic effect, sewage sludge ash (SSA) was used as main material to produce a sewage sludge ash foamed lightweight material (SSAFLM). Firing tests were conducted at different temperatures. This was to study how the use of sewage sludge ash (SSA) improved the thermal properties and sintering effects of cement-base materials, and to evaluate the feasibility of using SSA to improve the soundness of cement-base materials under high temperature. The experimental results revealed that when the sintering temperature was lower than 600 °C, the engineering properties and microstructure of SSAFLM were mainly affected by dewatering and hydrates decomposition. However, when the temperature was over 600 °C, the results were chiefly affected by sintering effects. At high temperatures, the more SSA was used, less crack formation resulted. Moreover, after fired at 1093 °C for 4 h, the compressive strength was improved by 44%, and the total pore volume decreased by 30% in average.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

The effect of zinc oxide additions on the performance of calcined sodium montmorillonite and illite shale supplementary cementitious materials

The objectives of this study were to use activation treatments on sodium montmorillonite and illite shale, to alter early hydration or later pozzolanic reactivity when used as supplementary cementitious materials (SCMs). For comparison purposes, treatment methods were also applied to the highly reactive pozzolan, metakaolin, and the inert filler, quartz. Activation treatment strategies included the addition of 0.15 wt% zinc oxide and the use of thermal treatments to the SCMs at temperatures of 650 °C, 830 °C and 930 °C. The use of zinc oxide additions increased the early hydration rate of SCM-containing pastes, yet introduced a chemical retardation and negatively impacted early compressive strengths. Moreover, the results suggest that retardation was inversely correlated with the pozzolanic reactivity of the SCM used. Thermal treatment methods were effective at influencing the SCM pozzolanic reactivity, with montmorillonite calcined at 830 °C and illite calcined at 930 °C behaving as late-reacting pozzolans. SCMs calcined at these temperatures resulted in higher 90 day compressive strengths compared to mortars containing the quartz filler. Overall, this study provides insight into different strategies that maybe used to enhance the reactivity of impure calcined clays in order to facilitate their acceptance into the concrete industry.     

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200 °C for 60 min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600 °C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400 °C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

Effect of heat treatment on mechanical properties of low alloy steel foams

Effect of heat treatment on compressive properties of low alloy steel foams (Fe–1.75 Ni–1.5 Cu–0.5 Mo–0.6 C) having porosities in the range of 47.4–71.5% with irregular pore shape, produced by the space holder-water leaching technique in powder metallurgy, was investigated. Low alloy steel powders were mixed with different amounts of space holder (carbamide), and then compacted at 200 MPa. Carbamide in the green compacts was removed by water leaching at room temperature. The green specimens were sintered at 1200 °C for 60 min in hydrogen atmosphere. Sintered compacts were heat treated by austenitizing at 850 °C for 30 min and then quenched at 70 °C in oil and tempered at 210 °C for 60 min. In this porosity range, compressive yield strengths of as-sintered and heat treated specimens were 28–122 MPa and 18–168 MPa, respectively. The resultant Young’s moduli of the as-sintered and heat treated specimens were 0.68–3.12 GPa and 0.47–3.47 GPa, respectively. The heat treatment enhanced the Young’s modulus and compressive yield strength of the foams having porosities in the range of 47.4–62.3%, as a consequence of matrix strengthening. However, the compressive yield stress and Young’s modulus of the heat treated foam having 71.5% porosity were lower than that of the as-sintered foam’s, as a result of cracks in the structure. The results were discussed in light of the structural findings.     

Reuse of water purification sludge as raw material in cement production

The feasibility of partial replacement of siliceous raw material for cement production with water purification sludge (WPS) was investigated by X-ray diffraction, free-lime analysis, compressive strength testing and toxicity characteristics leaching procedure (TCLP). It is found that WPS has no negative effects on the consumption of free lime and the formation of clinker minerals. The samples with WPS from 4 to 10 wt.% have higher 3 days and 7 days strengths than the control. After 28 days, however, only WPS replacements <7% increased the strength of samples. It is noteworthy that heavy metals in WPS were almost completely incorporated into the clinkers, and up to 28 days the heavy metals were not detected in the leachates. From the above results of clinker minerals, compressive strength and leaching tests, it can be concluded that WPS has the potential to be utilized as an alternative raw material in cement production.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Concrete mixtures incorporating synthesized sulfonated acetophenone–formaldehyde resin as superplasticizer

Polymers in concrete have received considerable attention over the past 25 years. Water-soluble sulfonated acetophenone–formaldehyde (SAF) resin was produced in the laboratory from the reaction between acetophenone–formaldehyde, and sodium bisulfite. Its performance as a concrete admixture was evaluated through its effect on the (w/c) ratio, air content, setting time, compressive strength at different ages, water absorption and permeable pores. Also, the performance of the concrete when subjected to acidic environment using sulfuric acid (pH = 4), and sulphate attack using magnesium sulphate (pH = 6.5) were investigated. SAF resin could be classified as a high-range water reducer with retarding effect (Type F and G according to ASTM C494). It was found that concrete mixtures incorporating SAF resin-based admixture yielded higher compressive strength results compared with the control concrete mixtures, as well as they are more resistant to aggressive environments investigated due to the higher resistance to water movement.     

Combined effects of milling and calcination methods on the characteristics of nanocrystalline barium titanate

Barium titanate (BT) nanoparticles were synthesized by high-energy planetary milling technique. Wet milling and dry milling effects were compared. The milled powders were calcined at 1000 °C by microwave and conventional heating methodologies. The calcined powders were characterized by XRD, VP-SEM, EDX, BET, TGA and laser Raman spectroscopy techniques. Dry milled and microwave calcined BT showed the highest extent of tetragonality value of 1.021. VP-SEM micrograph confirmed the tetragonal morphology of microwave calcined BT(s) with an average grain size of 81 nm. Raman Spectra corroborated well with the XRD results. Wet milled and microwave calcined powders showed relatively higher residual hydroxyl ion contamination than that of the dry milled powders. Dry milled and microwave calcined powders showed superior room temperature dielectric constant value with relatively lower dielectric loss tangent value which are very much essential for the fabrication of multi layered ceramic capacitors.     

Lightweight geopolymer concrete containing aggregate from recycle lightweight block

In this research, the properties of lightweight geopolymer concrete containing aggregate from recycle lightweight block were studied. The recycle block was crushed and classified as fine, medium and coarse aggregates. The compressive strength and density with various liquid alkaline/ash ratios, sodium silicate/NaOH ratios, NaOH concentrations, aggregate/ash ratios and curing temperatures were tested. In addition, porosity, water absorption, and modulus of elasticity were determined. Results showed that the lightweight geopolymer blocks with satisfactory strength and density could be made. The 28-day compressive strength of 1.0–16.0 MPa, density of 860–1400 kg/m³, water absorption of 10–31% and porosity of 12–34%, and modulus of elasticity of 2.9–9.9 GPa were obtained. It can be used as lightweight geopolymer concrete for wall and partition.     

Increasing the reactivity of metakaolin-cement blends using zinc oxide

This study aimed to improve the reactivity of metakaolin-cement mixtures using ZnO additions. Kaolinite samples with 0.1–1 wt% ZnO were calcined at temperature intervals of 50 °C from 500 to 650 °C for 1 h. The resulting metakaolins were examined for structural changes after calcination and for their pozzolanic reactivity, influence on the hydration behavior of cement pastes, and impact on the compressive strength of mortar cubes. ZnO behaved as a delayed accelerator for cement paste. However, when ZnO was combined with highly amorphous metakaolin, chemical retardation was eliminated while acceleration was maintained. Such systems also had increased 28-day compressive strengths. ZnO additions did not affect the degree of dehydroxylation or the pozzolanic reactivity of the metakaolin. These results could facilitate the use of less pure calcined clays as SCM by providing a mechanism for improving reactivity and may also impact the ability to use zinc-contaminated materials in concrete.     

Compressive performance of laminated bamboo

This study investigated the compressive performance of 24 laminated bamboo specimens made from three different growth portions of the source bamboo. The cross-section of each specimen was 100 mm × 100 mm. The load–strain and load–displacement relationships are obtained from compression tests, and the detailed failure modes, compressive strength and elastic modulus for all specimens are reported. The results show that the mean compressive strength increases with growth portion height, but that the variation in compressive strength also increases with growth portion height. The net result is that the characteristic strength (typically used in the design process) decreases slightly with growth portion height, but not significantly. In contrast, laminated bamboo manufactured from the middle growth portion exhibits the highest elastic modulus, with the variation again increasing with height. Although the source growth portion has a clear effect on the behaviour of laminated bamboo under compression, the paper concludes that the effect is not significant from a design perspective. The results of all the tests are combined to produce a model stress–strain relationship suitable for predicting the performance of laminated bamboo under compression for design purposes. The stress–strain relationship shows that under compression laminated bamboo fails in a ductile manner. Based on the compressive properties obtained in this research, laminated bamboo is a suitable construction material for engineering structures.     

Synthesis of nanocomposite powders of γ-alumina-carbon nanotube by sol–gel method

The nanocomposite powders of γ-alumina-carbon nanotube were successfully synthesized by a sol–gel process. The homogeneous mixture of carbon nanotubes and alumina particles was obtained by mixing the carbon nanotubes within alumina solution and followed by heating into gel. The resultant gel was dried and calcined at 200 °C into boehmite-carbon nanotubes composite powders. The mean particle size of synthesized boehmite was of the order of 4 nm. The boehmite-carbon nanotubes composite powders were calcined at different temperatures and XRD investigations revealed that as the amount of carbon nanotube increases, γ- to α-alumina phase transformation is completed at higher temperatures. The specific surface area and mean particle size of resultant nanocomposite powders increased and decreased, respectively by increasing the content of carbon nanotubes.     

Workability and strength of coarse high calcium fly ash geopolymer

In this paper, the basic properties viz., workability and strength of geopolymer mortar made from coarse lignite high calcium fly ash were investigated. The geopolymer was activated with sodium hydroxide (NaOH), sodium silicate and heat. The results revealed that the workable flow of geopolymer mortar was in the range of 110 ± 5%–135 ± 5% and was dependent on the ratio by mass of sodium silicate to NaOH and the concentration of NaOH. The obtained compressive strength was in the range of 10–65 MPa. The optimum sodium silicate to NaOH ratio to produce high strength geopolymer was 0.67–1.0. The concentration variation of NaOH between 10 M and 20 M was found to have a small effect on the strength. The geopolymer samples with high strength were obtained with the following practices: the delay time after moulding and before subjecting the sample to heat was 1 h and the optimum curing temperature in the oven was 75 °C with the curing duration of not less than two days.     

Effect of specimen size and shape on compressive strength of concrete containing fly ash: Application of genetic programming for design

The use of fly ash as a mineral admixture in the manufacture of concrete has received considerable attention in recent years. For this reason, several experimental studies are carried out by using fly ash at different proportions replacement of cement in concrete. In the present study, the models are developed in genetic programming for predicting the compressive strength values of cube (100 and 150 mm) and cylinder (100 × 200 and 150 × 300 mm) concrete containing fly ash at different proportions. The experimental data of different mixtures are obtained by searching 36 different literatures to predict these models. In the set of the models, the age of specimen, cement, water, sand, aggregate, superplasticizers, fly ash and CaO are entered as input parameters, while the compressive strength values of concrete containing fly ash are used as output parameter. The training, testing and validation set results of the explicit formulations obtained by the genetic programming models show that artificial intelligent methods have strong potential and can be applied for the prediction of the compressive strength of concrete containing fly ash with different specimen size and shape.