Heat Curing Conditions Research Articles

Effects of silica fume and rice husk ash contents on engineering properties and high-temperature resistance of slag-based prepacked geopolymers

Geopolymer slurries can be favored to achieve a sustainable approach in prepacked aggregate concretes. This study presented here investigated experimentally the effect of silica fume (SF) and rice husk ash (RHA) on the high-temperature resistance of slag-based sustainable prepacked geopolymers. In the production of prepacked aggregate geopolymers (PAGs), ground granulated blast furnace slag (GGBFS) was utilized as the main aluminosilicate-rich precursor material, and SF and RHA were replaced with GGBFS in various contents including 7.5 % and 15 %. The physical, mechanical, and microstructural properties of specimens cured at 35 °C and 70 °C for 8 h were determined comparatively. Residual compressive strength and mass loss of mixtures exposed to elevated temperatures (150 °C, 300 °C, and 600 °C) were determined to observe high-temperature effects. The results revealed that the properties of PAGs were affected considerably by curing temperature and precursor type. The maximum oven-dry density of 2244 kg/m3 with RHA content of 7.5 % was obtained at 70 °C curing temperature. Specimens produced with RHA tended to absorb more water under both heat curing conditions and the highest water absorption of 10.2 % with RHA content of 7.5 % was obtained at 35 °C curing temperature. The compressive strength of PAGs varied between 13.7 and 28.10 MPa, and flexural strengths varied between 1.48 and 2.74 MPa. Increasing curing temperature improved the strength properties of PAGs, and in general, the 8-h compressive and flexural strength values of SF samples were relatively higher. The application of elevated temperature to the PAG mixtures caused a significant reduction in both compressive strength and mass loss. Among the specimens cured at 35 °C, the specimens with RHA showed relatively better high-temperature performance in terms of compressive strength, while the specimens with SF cured at 70 °C showed better performance. PAG specimens produced with RHA showed the best high-temperature performance against mass loss. According to the results obtained in the given study, these recycled wastes could be used to improve the physico-mechanical properties and high-temperature performance of slag-based PAGs.

Properties of Geopolymer Mixtures Incorporating Recycled Ceramic Fines.

This research aimed to optimize the production conditions for geopolymer matrices by investigating the combination of heat curing conditions and the incorporation of recycled ceramic fines (CFs) as a partial replacement material for fly ash (FA). The obtained physical and mechanical properties of the composites confirmed the positive impact resulting from increasing the curing temperature from 65 °C to 85 °C and using CFs in the amount of 37.5% as a replacement for FA. The results were from laboratory tests performed to evaluate compressive strength, bending strength, bulk density, and water absorption of the geopolymer mixes. In addition, microscopic observations and porosity assessment were also performed, which confirmed that a further increase in the replacement of FA by CFs causes an increase in the porosity of the mixes and, thus, a decrease in all the assessed properties that are relevant to their practical use.

Characterization of Waste Clay Brick Powder and its Effect on the Mechanical Properties and Microstructure of Geopolymer Mortar

Fly ash is known as a common geopolymer precursor. However, it is important to search for suitable alternatives as the availability of fly ash will reduce with the move to more renewable energies. This paper evaluates the feasibility of using waste clay brick powder (WCBP) as a partial alternative for fly ash in geopolymer mortars with ground granulated blast furnace slag (GGBFS), under ambient and heat curing conditions. The physical, mechanical, and mineralogical properties of geopolymer mortar with 10 to 40% WCBP were investigated. Microstructural properties of WCBP and geopolymer mortars were investigated using X-ray fluorescence (XRF), X-ray diffraction (XRD), tescan integrated mineral analyzer (TIMA), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Reductions of the flow of fresh mortar were observed with the increase of WCBP. The highest 28 days compressive strengths were obtained in the mortars containing 40% WCBP, both at ambient and heat curing conditions. Microstructural analysis highlighted compact structure and reduced porosity, which are attributed to the role of WCBP in enhancing fly ash-GGBFS mortar properties by promoting geopolymer gel formation.

Factors affecting compressive strength and expansion due to alkali-silica reaction of fly ash-based alkaline activated mortar

The development of environmentally friendly alkaline-activated materials (AAMs) holds promise, as AAMs can be derived from waste materials. This study aims to investigate the factors influencing (i) compressive strength and (ii) expansion due to alkali-silica reaction (ASR) in AAMs. These factors include alkaline concentration, heat curing conditions, fineness of fly ash, and the liquid alkaline-to-binder (L/B) ratio. The findings indicate that the higher concentrations of NaOH solution led to an increase in AAM compressive strength due to the enhanced dissolution and polymerization rates in a more alkaline environment. Heat curing stimulated chemical reactions and structure formation, while the reduced water content resulted in lower porosity and higher compressive strength in the hardened cement. Finer fly ash yielded greater compressive strength than coarser ash, as its smaller spherical particles contributed to denser and firmer structures. The presence of calcium minerals, from both Ordinary Portland Cement (OPC) and high-calcium fly ash, bolstered the strength of hardened products. Moreover, calcium minerals like CaO, Ca(OH)2, and CaSO4 were found to induce ASR expansion by promoting gel formation, leading to later-stage expansion in the hardened cement or concrete. However, finely milled fly ash as a precursor significantly reduced ASR expansion in AAMs, by approximately 40% compared to ordinary Portland cement. This study provides valuable insights for civil engineers for better understanding of AAM behavior and makes contributions to the safety and sustainability of cement and concrete systems.

Study on Improving Measures of Mechanical Properties of Geopolymer Materials and Its Effect on CO2 Emission.

Using construction and demolition waste composites (CDWC) and fly ash (FA) to replace cement to produce concrete can reduce CO2 emissions. However, the CDWC-based geopolymer materials have two imperfections: the compressive strength is prone to decrease with the increase of curing age (strength shrinkage) under heat curing conditions, and the strength develops slowly under ambient curing conditions. To solve the problems of these materials, on the one hand, we designed an experiment of preparing CDWC-based geopolymer concrete (CDWGC) with pretreated CDWC at different high temperatures. We analyzed the influence of different pretreatment temperatures on the mechanical properties of CDWGC through compressive strength, SEM-EDS and XRD. On the other hand, we added CaO to improve the mechanical properties of CDWC-based geopolymer paste (CDWGP) under ambient curing conditions. Further, the CO2 emissions of pretreating CDWC and adding CaO were calculated by life cycle assessment (LCA). The results show that: (1) Pretreatment of CDWC can effectively solve the problem of CDWGC strength shrinkage. (2) The compressive strength of CDWGP cured at ambient can be significantly improved by adding CaO, and the compressive strength can be increased by 180.9% when the optimum content is 3%. (3) Adding CaO had less impact on CO2 emissions, a low-carbon way to improve its strength effectively.

The study on various temperature condition of fly ash based geopolymer mortar

The present research investigated the curing conditions (ambient and heat curing) and the duration of heat curing which is considered as significant criteria affecting the mortar strength. The geopolymer (GP) sample was cured at several heating temperatures, which were ambient, 60, 80, and 100 °C for a curing time of 24 h in the oven. The samples were then stored at room temperature until the day of testing. Compressive strength (CS) was used to evaluate the mechanical characteristics of GP mortar. Mortar control specimens that hardened at room temperature were used for comparison. The outcomes were established using specimens ages 3, 7, 28, 56, and 90 days after the curing procedure. The study reveals that the CS of GP mortar under heat curing conditions develops polymerization faster as the temperature rises. Comparing curing at ambient temperature to elevated temperatures, it can be determined that temperature has a significant effect in promoting the GP mortar strength increase. In comparison to all other curing conditions, oven curing at 80 °C for 24 h obtained the highest CS (32 MPa) at the age of 90 days. The partial replacement of GGBS under ambient curing conditions yielded a maximum CS of 35 MPa.

Performance evaluation on engineering properties of sodium silicate binder as a precursor material for the development of cement-free concrete

In emerging economies, huge stocks of industrial wastes are dumped in open landfills. Such wastes serve as a source for environmental pollution. Some of these materials such as Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBFS), Rice Husk Ash (RHA), and Palm Oil Fuel Shell Ash (POFA) can be used as binder materials to produce concrete mix. Aim of the study is to effectively utilize the Municipal Solid Waste (Sodium Silicate Waste (SSW)) powder as a partial replacement for FA in the development of Geopolymer Concrete (GPC). GPC requires heat curing for the attainment of early age strength. The development of GPC under heat curing conditions is a hard process in practice. To overcome such circumstances, an attempt was made to develop the GPC under ambient curing conditions with the aid of SSW. The influence of SSW on strength gain and microstructural characteristics of GPC is investigated. Mechanical properties of GPC such as compressive strength, tensile strength, and flexural strength are reported and discussed. This study focuses on the assessment of mechanical and microstructure characterization of eco-efficient GPC developed with SSW. The required optimum quantity of binder, alkali activator, alkaline liquid to binder ratio and aggregates was determined by appropriate trials. Following the properties of SSW, it is realistic to substitute up to 50% of SSW as the resulting binder mix falls within the requirements of the analyzed mix. Increase in the percentage of SSW decreases the fresh properties of GPC, such as setting time and workability; mix with 50% SSW exhibited the lowest initial and final setting time i.e., 77% and 81% than the control mix. Contrastingly, inclusion of SSW content enhances the mechanical properties of the mix. 12SSW50 mix produces the maximum compressive, tensile and flexural strength of 40.16 MPa, 2.8 MPa, and 4.18 MPa, respectively. Mix with 8 M concentration comprising 50% SSW possess higher cost efficiency than the mix with higher alkaline content. The main significance of this research work is, SSW can be used as a precursor material as an alternative for cementitious binder with better efficiency in terms of strength, microstructure, and sustainability. Therefore, GPC produced with SSW is an eco-friendly and sustainable building material. Effective use of waste materials such as fly ash and SSW for the development of GPC is another major research focus in the proposed investigation.

Immobilization mechanism of radioactive borate waste in phosphate-based geopolymer waste forms

The solidification of radioactive borate waste (BW), which contains a high concentration of boron ions using cement waste forms is challenging because soluble borate hinders the cement hydration reaction. Here, BW was immobilized using a phosphate-based geopolymer, and the phase change of BW in the geopolymer was investigated. The geopolymers could solidify BW up to 50 wt% depending on the water content and heat curing conditions. In geopolymers cured at high temperatures (60 and 90 °C), the 7-day compressive strength increased as the BW waste loading increased up to 40 wt%. Heat curing promoted geopolymerization and the precipitation of amorphous boron phosphate, leading to an increase in the compressive strength. The formation of a new amorphous boron phosphate phase was confirmed by performing XRD, MAS NMR, and SEM analyses of the geopolymers and reaction products. These results can improve our understanding of the immobilization mechanism of BW in phosphate-based geopolymers.

Development and strength assessment of eco-friendly geopolymer concrete made with natural and recycled aggregates

Purpose This study aims to develop geopolymer concrete (GPC) using manufactured sand (M-sand) and recycled concrete aggregate (RCA) under different curing conditions. GPC is a sustainable construction material developed with industrial waste products such as fly ash to eliminate the use of cement in the production of concrete. GPC requires heat curing for the attainment of early age strength. The development of GPC under heat curing conditions is a hard process in practice. To overcome such circumstances, an attempt was made to develop the GPC under different curing conditions with the aid of coarse aggregate (CA) and RCA. The influence of different curing conditions on strength gain and microstructural characteristics of GPC is investigated. Mechanical properties of GPC such as compressive strength, tensile strength, flexural strength and elastic modulus are reported and discussed. Design/methodology/approach This study focuses on the assessment of mechanical and microstructure characterization of eco-efficient GPC developed with natural CA and RCAs. The required optimum quantity of binder, alkali activator, alkaline liquid to binder ratio and aggregates was determined by appropriate trials. Three types of curing methods, namely, ambient, oven and water, were used for the development of GPC mixes. Following the properties of RCA, it is realistic to substitute up to 40% of coarser aggregates as the resulting aggregate mix falls within the requirements of the analyzed mix. Findings Special attention is required for the mix with RCA because the mix’s consistency is affected by the high water absorption of the RCA mix. GPC specimens cured at ambient and water conditions exhibited marginal variation in the compressive strength for both CA and RCA. The compressive strength of GPC mixes prepared with RCA was marginally higher than that of the GPC made with CA under different curing regimes. RCA can be used as a sustainable material in lieu of CA in GPC. Originality/value The main significance of this research work is to develop the optimal mix design with appropriate mix proportion. The present study proposes a satisfactory methodology that enhances the mechanical strength of GPC as the guidelines are not available in the standards to address this problem. Effective use of waste materials such as fly ash and recycled aggregate for the development of GPC is another major research focus in the proposed investigation.

Chloride diffusivity and mechanical performance of UHPC with hybrid fibers under heat treatment regime

Steel fibers are an inseparable part of ultra high performance concretes (UHPC). The effects of steel fibers have been widely studied in recent years; however, the hybridization of steel fiber with different types of fibers and their effect on the properties of UHPC has not been completely investigated. In addition, under thermal treatment, which is a common way for curing UHPC elements, the use of hybrid fibers may change the concrete characteristics. In this paper, mixtures containing different types of fibers in the hybrid forms were produced and the specimens were cured under normal and heat curing conditions. To characterize the effect of hybrid fibers on UHPC mixes under different curing regimes, the workability, compressive strength, flexural parameters (including first crack strength, module of rupture, load-deflection curves and toughness index) and scanning electron microscope (SEM) microstructural analyses were investigated. The results revealed that the concrete mix with 2.5 % mono fiber had higher flexural performance than the hybrid mixes. However, the use of steel fiber with the volume fraction of 1.5 % was more effective in improving the compressive strength. Higher flexural load-bearing capacity was observed for the hybrid mixes with macro fibers of Barchip and Kortta. The UHP-FRCs containing Barchip and Kortta fibers, due to the permeable internal structure, had lower chloride resistance than the 2.5 % of steel fiber concrete. In addition, the chloride migration coefficients of the hybrid mixtures with the glass, carbon and polypropylene fibers were about 5 times higher than those of the mix with 1.5 % steel fiber. Compared with normal curing condition, the load drop after cracking was more visible for the mixes cured under heat curing, which could be limited by using high-volume steel fiber and hybrid micro fibers. Furthermore, applying thermal treatment for curing concrete mixes led to lower chloride ion penetration; the enhancement was more pronounced for the hybrid mixes with micro fibers of glass, carbon and polypropylene.

Effect of curing conditions on the water vapor sorption behavior of melamine formaldehyde resin and resin-modified wood

Impregnation modification of wood with melamine formaldehyde resin reduces the adverse effects caused by moisture uptake, but the underlying modes of action are not fully understood. The present study showed that it is crucial to understand the sorption behavior of the pure resin when interpreting the behavior of resin-modified wood. Furthermore, the applied heat-curing conditions had a significant effect on the moisture uptake of resin-modified wood. At the same resin loads, dry curing conditions were more effective in causing a cell wall bulking effect than wet curing conditions. This reduced the water-accessible cell wall pore volume in dry cured wood and counterbalanced the moisture uptake by the resin. Deuterium exchange measurements suggested that the occupancy of cell wall pores reduced the number of simultaneously active sorption sites. However, there was no evidence that a swelling restraint or reduced mechanical relaxation affected the water sorption of resin-modified wood significantly.

Distribution and curing reactions of melamine formaldehyde resin in cells of impregnation-modified wood

Wood modification improves the properties of wood as a building material by altering the wood structure on a cellular level. This study investigated how dimensional changes of wood on a macroscopic scale are related to the cellular level chemical changes on the micron level after impregnation modification with melamine formaldehyde (MF) resin under different heat curing conditions. Our results showed that the curing conditions affected the polycondensation reactions and the morphological structure of the MF resin within the cell lumen. The diffusion of the resin into the cell wall was estimated based on the triazine ring vibration of melamine in the Raman spectrum at 950–990 cm−1. Thereby, it was shown that macroscopic changes in wood dimensions do not provide a reliable estimate for the cell wall diffusion of the resin. The removal of cell wall constituents during the modification, which was facilitated by the alkaline pH of the impregnation solution, counterbalanced the cell wall bulking effect of the resin. This was particularly evident for wet cured samples, where diffusion of MF resin into the cell wall was observed by confocal Raman microscopy, despite a reduction in macroscopic wood dimensions.

Heat Curing Efficiency Estimation of Concrete with Superplastificators on Polycarboxylates Basis

The influence of superplastificators on polycarboxylates basis upon forming concrete mechanical and physical properties was estimated under heat curing. Heat curing is most effective for rapid concrete hardening. But simultaneously with concrete strength development heat curing may cause destruction, decreasing the most important concrete properties. It was established that steam cured self-compacting concrete with superplastificators on polycarboxylates basis is most effective at low temperature heat curing conditions. The rational concrete heat curing temperature mode should be chosen according to quality parameters estimated during experiments.

How to understand the effects of heat curing conditions on the morphology and performance of polypiperazine-amide NF membrane

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na2SO4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane.

Chloride diffusion resistance and chloride binding capacity of fly ash-based geopolymer concrete

This study evaluated the chloride diffusion resistance of low-calcium fly ash-based geopolymer concrete through electrical and bulk diffusion techniques. The geopolymer concretes were prepared using 12 different heat curing conditions; three temperatures of 60, 75 and 90 °C and four curing durations of 8, 12, 18 and 24 h, as well as ambient curing. The mechanical and transport properties and microstructural characteristics of the geopolymer concretes were examined. NT BUILD 492 chloride migration and ASTM C1556 bulk diffusion tests were carried out. Results showed that the chloride diffusion resistance and the chloride binding capacity of fly ash-based geopolymer concrete is very low. The fly ash-based geopolymer concrete appears to be suitable for applications where there are little or no chloride-related durability concerns.

Comparative shrinkage behavior of ultra-high-performance fiber-reinforced concrete under ambient and heat curing conditions

This study aims to investigate the effect of curing conditions on the free shrinkage behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). For this study, a number of exposed and sealed prismatic UHPFRC samples for drying and autogenous shrinkage measurements were fabricated and tested using two different types of embedded strain gauges. Several other tests, including mechanical tests, X-ray diffraction (XRD), and mercury intrusion porosimetry analyses, were also performed. Test results indicate that steam curing with heat (90 °C, referred to as heat curing) was effective to improve the mechanical properties of UHPFRC at an early age in terms of strength, elastic modulus, and fracture energy absorption capacity. The larger quantities of C-S-H and much smaller total cumulative pore volume were obtained for the steam-cured specimens, compared to those for the ambient-cured specimens. The ultimate autogenous shrinkage of UHPFRC was insignificantly affected by the curing conditions, whereas heat curing accelerated the shrinkage development as compared to ambient curing. In particular, there was no increase of shrinkage strains for UHPFRC after heat curing was finished. The ultimate drying and autogenous shrinkage of UHPFRC were found to be approximately −45 με and −450 με, respectively. Based on literature review, an optimized model was suggested, and the autogenous shrinkage developments of UHPFRC at both ambient and heat curing conditions were successfully predicted based on the equivalent age method.

Steel fibre reinforced geopolymer concrete (SFRGC) with improved microstructure and enhanced fibre-matrix interfacial properties

Geopolymers are aluminosilicate materials formed by mixing by-product materials with alkaline solutions, and which have several desirable properties compared to Portland cement concrete in terms of strength and durability. Most of the previous research on steel fibre reinforced geopolymer concrete (SFRGC) has focused on the properties of single or binary mixes hardened under heat curing conditions, which is a severe limitation for on-site, cast-in-place applications. In the current study, a novel plain and steel fibre reinforced geopolymer concrete (SFRGC), containing various types of commercial Silica Fume (SF) (densified, undensified and slurry silica fume) and varying Ground Granulated Blast Furnace Slag (GGBS) content in a ternary binder mixture, cured under ambient (room) temperature has been examined. An extensive experimental investigation was conducted to evaluate the fresh properties, mechanical characteristics and microstructure of the examined material. The experimental results indicate that the mechanical characteristics of all the examined mixes are enhanced by increasing the GGBS content, in both plain and steel fibre reinforced geopolymer concrete. Geopolymer concrete with undensified silica fume showed better mechanical strength compared to that with densified and slurry SF, due to the agglomeration and ineffective dispersion of the latter fume types. SEM microstructural observations and porosity measurements were also conducted. The results indicate that the inclusion of silica fume and increasing GGBS content leads to higher pozzolanic activity and pore infilling, providing relatively homogeneous, compact and dense microstructures and subsequently improved mechanical properties.

Suitability of heat-cured low-calcium fly ash-based geopolymer concrete for precast applications

This paper discusses the advantages of using low-calcium fly ash (FA)-based geopolymer concrete (GPC) for precast applications when high early-age strength is required. Heat curing is known to be the reaction accelerator for both Portland cement (OPC) concrete and the newly emerged GPC. Here, the influence of 12 different heat-curing regimes, as well as internal curing, on mechanical properties of an FA-based GPC is investigated. The curing regimes include three temperatures of 60, 75 and 90°C, and four curing durations of 8, 12, 18 and 24 h. Results are compared with that of OPC concrete counterpart, with the same amount of binder and aggregate. Test results show that, in optimum heat-curing conditions, GPC can achieve more than 90% of its 28 d compressive strength after 1 d, compared to only 55% to 71% for normal concrete. The optimum heat-curing regime for GPC, combining best performance and energy efficiency, is found to be 75°C for 18 h. Contrary to conventional concrete, heat curing has no detrimental effect on the long-term compressive strength of GPC. It is concluded that, for precast applications, FA-based GPC appears to perform better than OPC concrete in terms of both early and long-term compressive strength using the same amount of binder.

Bond strength between blended slag and Class F fly ash geopolymer concrete with steel reinforcement

Abstract In this paper, geopolymer concrete bond with both deformed and smooth reinforcing steel bars is investigated using the standard RILEM pull-out test. The geopolymer binder is composed of 85.2% of low calcium fly ash and 14.8% of ground granulated blast furnace slag (GGBFS). The tests were aimed to assess the development of the bond strength from 24 h to 28 days after casting, with different heat curing conditions. The results show that 48 h of heat curing at 80 °C is required in order to obtain similar or better performances to those of the reference 45 MPa OPC concrete. The 28-day bond strength and the overall bond stress–slip behaviour of the geopolymer concrete were similar to those previously reported for OPC-based concretes. Providing intensive heat curing, high early bond strength can be achieved showing that Class F fly ash geopolymer concrete is well suited for precast applications.

Using Ozawa method to study the curing kinetics of electrically conductive adhesives

In this paper, we fabricated electrically conductive adhesives using vinyl ester resin and micro silver flakes, and then cured the adhesives by heat without any catalysts or initiators. The curing temperature was above 200 °C, and the curing time about 30 min. Under these heat curing conditions, the double bonds in the adhesives reached a high conversion (α) around 98.88 % calculated from the Fourier transform infrared spectroscopy analysis. The curing kinetics of heat curing products was studied using Ozawa method and deduced by assuming a constant activation energy (E). The curing kinetic equation was obtained as dα/dt = e17.70(1 − α)1.19α0.41e(−94.32)/RT) with E = 94.32 kJ mol−1. The heat curing followed the shrinking core model from the resin-particle system. The data calculated from the kinetic equation agreed well with the experimental data, showing that the Ozawa method could evaluate the curing kinetics effectively. Furthermore, a comprehensive and in-depth understanding of the curing kinetics of heat curing electrically conductive adhesives has been achieved with this Ozawa method.