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The purpose of this paper is to investigate the effect of the replacement of natural coarse aggregate (NCA) with different percentages of recycled coarse aggregate (RCA) on properties of low calcium fly ash (FA)-based geopolymer concrete (GPC) cured at oven temperature. Further, this paper aims to study the effect of partial replacement of FA by ground granulated blast slag (GGBS) in GPC made with both NCA and RCA cured under ambient temperature curing.

M25 grade of ordinary Portland cement (OPC) concrete was designed according to IS: 10262-2019 with 100% NCA as control concrete. Since no standard guidelines are available in the literature for GPC, the same mix proportion was adopted for the GPC by replacing the OPC with 100% FA and W/C ratio by alkalinity/binder ratio. All FA-based GPC mixes were prepared with 12 M of sodium hydroxide (NaOH) and an alkalinity ratio, i.e. sodium hydroxide to sodium silicate (NaOH:Na₂SiO₃) of 1:1.5, subjected to 90^°C temperature for 48 h of curing. The NCA were replaced with 50% and 100% RCA in both OPC and GPC mixes. Further, FA was partially replaced with 15% GGBS in GPC made with the above percentages of NCA and RCA, and they were given ambient temperature curing with the same molarity of NaOH and alkalinity ratio.

The workability, compressive strength, split tensile strength, flexural strength, water absorption, density, volume of voids and rebound hammer value of all the mixes were studied. Further, the relationship between compressive strength and other mechanical properties of GPC mixes were established and compared with the well-established relationships available for conventional concrete. From the experimental results, it is found that the compressive strength of GPC under ambient curing condition at 28 days with 100% NCA, 50% RCA and 100% RCA were, respectively, 14.8%, 12.85% and 17.76% higher than those of OPC concrete. Further, it is found that 85% FA and 15% GGBS-based GPC with RCA under ambient curing shown superior performance than OPC concrete and FA-based GPC cured under oven curing.

The scope of the present paper is limited to replace the FA by 15% GGBS. Further, only 50% and 100% RCA are used in place of natural aggregate. However, in future study, the replacement of FA by different amounts of GGBS (20%, 25%, 30% and 35%) may be tried to decide the optimum utilisation of GGBS so that the applications of GPC can be widely used in cast in situ applications, i.e. under ambient curing condition. Further, in the present study, the natural aggregate is replaced with only 50% and 100% RCA in GPC. However, further investigations may be carried out by considering different percentages between 50 and 100 with the optimum compositions of FA and GGBS to enhance the use of RCA in GPC applications. The present study is further limited to only the mechanical properties and a few other properties of GPC. For wider use of GPC under ambient curing conditions, the structural performance of GPC needs to be understood. Therefore, the structural performance of GPC subjected to different loadings under ambient curing with RCA to be investigated in future study.

The replacement percentage of natural aggregate by RCA may be further enhanced to 50% in GPC under ambient curing condition without compromising on the mechanical properties of concrete. This may be a good alternative for OPC and natural aggregate to reduce pollution and leads sustainability in the construction.

This paper aims to investigate the influence of post-curing temperature, post-curing time and gamma ray irradiation dose upon the tensile and compressive mechanical properties of the medical graded vat photopolymerization parts.

Medical graded vat photopolymerization specimens, made from photopolymer resin, were fabricated using bottom-up vat photopolymerization machine. Tensile and compressive tests were conducted to assess the mechanical properties. The specimens were categorized into uncured and post-curing groups. Temperature post-processing and/or gamma irradiation exposure were for post-curing specimens. The post-curing parameters considered included temperature levels of 50°C, 60°C and 70°C, with 1, 2, 3 and 4 h periods. For the gamma irradiation, the exposure doses were 25, 50, 75 and 100 kGy.

Post-curing improved the mechanical properties of medical graded vat photopolymerization parts for both tensile and compressive specimens. Post-curing temperature greater than 50°C or a prolonged post-curing period of more than 1 h made insignificant changes or deterioration in mechanical properties. The optimal post-curing condition was therefore a 50°C post-curing temperature with 1 h post-curing time. Exposure to gamma ray improved the compressive mechanical properties, but deteriorated tensile mechanical properties. Higher gamma irradiation doses could decrease the mechanical properties and also make the part more brittle, especially for doses more than 25 kGy.

The obtained results would be beneficial to the medical device manufacturer who fabricated the invasive temporary contact personalized surgical instruments by vat photopolymerization technique. In addition, it also raised awareness in excessive gamma sterilization in the medical graded vat photopolymerization parts.

The silicone modifications of two-component epoxy resin coatings are commonly built on epoxy resins rather than on epoxy curing agents. The silicone-modified epoxy curing agent system is rarely reported yet. This study aims to prepare the polysiloxane (PS)-modified waterborne epoxy coatings based on aqueous curing agents technology.

Waterborne epoxy curing agents with different contents of terminal epoxy PS were synthesized by reacting with triethylenetetramine, followed by incorporating of epoxy resin (NPEL-128) and polyethylene glycol diglycidyl ether. The waterborne epoxy coatings were prepared with the above curing agents, and their performance was investigated through thermogravimetric analysis, scanning electron microscopy, mechanical characterization, gloss measurement, chemical resistance test and ultraviolet (UV) aging experiment.

The results showed that the epoxy coating prepared by silicon-modified curing agent has higher gloss, better chemical resistance and UV resistance than the coating from unmodified curing agent with terminal epoxy PS and commercially available waterborne epoxy curing agent (Aradur 3986), as well as the competitive mechanical properties and heat resistance. Reduced water absorption on fibrous paper was also obtained with the help of silicon-modified curing agent.

These findings will be valuable for resin researchers in addressing the modification issues about waterborne epoxy resin and curing agent.

Microwave curing (MC) can facilitate rapid concrete repair in cold climates without using conventional accelerated curing technologies which are environmentally unsustainable. Accelerated curing of concrete under MC can contribute to the decarbonisation of the environment and provide economies in construction in several ways such as reducing construction time, energy efficiency, lower cement content, lower carbonation risk and reducing emissions from equipment.

The paper investigates moisture loss and pore properties of six cement-based proprietary concrete repair materials subjected to MC. The impact of MC on these properties is critically important for its successful implementation in practice and current literature lacks this information. Specimens were microwave cured for 40–45 min to surface temperatures between 39.9 and 44.1 °C. The fast-setting repair material was microwave cured for 15 min to 40.7 °C. MC causes a higher water loss which shows the importance of preventing drying during MC and the following 24 h.

Portland cement-based normal density repair mortars, including materials incorporating pfa and polymer latex, benefit from the thermal effect of MC on hydration, resulting in up to 24% reduction in porosity relative to normal curing. Low density and flowing repair materials suffer an increase in porosity up to 16% due to MC. The moisture loss at the end of MC and after 24h is related to the mix water content and porosity, respectively.

The research on the application of MC for rapid repair of concrete is original. The research was funded by the European commission following a very rigorous and competitive review process which ensured its originality. Original data on the parameters of porosity and moisture loss under MC are provided for different generic cementitious repair materials which have not been studied before. Application of MC to concrete construction especially in cold climates will provide environmental, economic and energy benefits.

This paper aims to investigate the bond strength of metakaolin-based geopolymer mortar with cement mortar.

The mortar-mortar bond strength is assessed by slant shear and split tensile tests; pure shear strength is evaluated by Mohr’s criterion for result validation. Metakaolin-based geopolymer mortar is cast over the cured cement mortar specimen with two levels of surface roughness: smooth or grooved interface. The influence of the alkaline solution to metakaolin ratio on geopolymer bond strength is studied. Compressive strength, ultrasonic pulse velocity, permeability and flow table tests are also performed.

The paper’s findings are highlighted as follows: (1) strong mortar-mortar bond properties achieved for geopolymer mortar in all tests and conditions and validated by Mohr’s criterion and pure shear, (2) a lower alkaline solution to metakaolin ratio achieves higher bond strength to Portland cement mortar and (3) geopolymer mortar has higher compressive strength and ultrasonic pulse velocity than cement mortar at all curing ages; additionally, it is more flowable and less permeable.

The full replacement of Portland cement with metakaolin, a more sustainable cementitious material, will contribute to the decarbonization of the construction industry.

Limited research has been carried out on the bond strength of metakaolin-based geopolymer mortar to Portland cement mortar. Also, computing the pure shear using Mohr’s circle criterion of metakaolin-based geopolymer to validate the results can be considered original.

This study aims to practically determine the optimum proportion of aggregates to attain the desired strength of geopolymer concrete (GPC) and then compare the results using established analytical particle packing methods. The investigation further aims to assess the influence of various amounts of recycled aggregate (RA) on properties of low-calcium fly ash-based GPC of grade M25.

Fine and coarse aggregates were blended in various proportions and the proportion yielding maximum packing density was selected as the optimum proportion and they were compared with analytical models, such as Modified Toufar Model (MTM) and J. D. Dewar Model. RAs for this study were produced in laboratory and they were used in various amounts, namely, 0%, 50% and 100%. 12M NaOH solution was mixed with Na₂SiO₃ in the ratio of 1:2. The curing of concrete was done at the temperatures of 60° and 90 °C for 24, 48 and 72h.

The experimentally obtained optimum proportion of coarse to fine aggregate was 60:40 for all amounts of RA. Meanwhile, MTM and Dewar Model resulted in coarse aggregate to fine aggregates as 40:60, 45:55, 55:45 and 55:45, 35:65, 60:40, respectively, for 0% 100% and 50% RAs. The compressive strength of GPC elevated with the increase in curing regime. In addition, the ultrasonic pulse velocity also displayed a similar trend as that of strength.

The GPC with 50% RAs may be considered for use, as it exhibited superior properties compared to GPC with 100% RAs and was comparable to GPC with natural aggregates. Furthermore, compressive strength is correlated with split tensile strength and ultrasonic pulse velocity.

This paper aims to compare the surface roughness and hardness of three commercially available self-curing acrylic resins for dental use, under different polymerization conditions.

A comparative in vitro study was conducted using a convenience sample of 12 × 5 × 2 mm blocks with n = 40 for each material (Nic Tone, Arias Plus and Orthocryl®), with subgroups according to the polymerization method: conventional (C) and polymerization under ambient conditions (A). The surface roughness of the materials was measured using a profilometer; hardness was measured with a portable hardness tester. Additionally, surface morphology as well as particles size and morphology were evaluated with scanning electron microscopy.

There were significant differences in roughness and hardness values between the three self-curing acrylic resins (p < 0.05), as well as within each self-curing acrylic resin according to the polymerization method used (p < 0.05). The samples polymerized with the conventional method presented lower surface roughness and hardness values.

This study provides scientific evidence of values not provided by manufacturers in relation to the surface roughness and hardness of these materials, and all of them met the ideal minimum values of surface roughness, regardless of the polymerization technique used.

The coal-based synthetic natural gas slag (CSNGS) is a solid waste remaining from the incomplete combustion of raw coal to produce gas. With the continuous promotion of efficient and clean utilization of coal in recent years, the stockpiling of CSNGS would increase gradually, and it would have significant social and environmental benefits with reasonable utilization of CSNGS. This study prepared a new geopolymer by mixing CSNGS with PC42.5 cement in a certain mass ratio as the precursor, with sodium hydroxide and sodium silicate solution as the alkali activators.

The formulation of coal-based synthetic natural gas slag geopolymer (CSNGSG) was determined by an orthogonal test, and then the strength mechanism and microstructure of CSNGSG were characterized by multi-scale tests.

The results show that the optimum ratio of CSNGSG was a sodium silicate modulus of 1.3, an alkali dosage of 21% and a water cement ratio of 0.36 and the maximum unconfined compressive strength of CSNGSG at 7 d was 26.88 MPa. The increase of curing temperature could significantly improve the compressive strength of CSNGSG, and the curing humidity had little effect on the compressive strength of CSNGSG. The development of the internal strength of CSNSG at high temperatures consumed SiO₂, Al₂O₃ and CaO and the intensity of corresponding crystalline peaks decreased.

Moreover, the vibration of chemical bonds in different wavenumbers also revealed the reaction mechanism of CSNSG from another perspective. Finally, the relevant test results indicated that CSNGS had practical application value as a raw material for the preparation of geopolymer cementing materials.

This study aims to investigate the properties of mortar made from a bottom ash substitute as a sustainable construction material. It is believed that the use of cement in concrete construction contributes to the release of carbon dioxide into the atmosphere, which has been a consistent increase in recent years. The utilization of bottom ash waste is expected to reduce pollution associated with cement production.

Bottom ash is used as replacement materials for cement and fine aggregate in the manufacture of mortar. Bottom ash substituted for cement of 10%, 20% and 30% of the total weight of the binder, whereas bottom ash substituted for the fine aggregate of 30%, 40% and 50% of the total weight of the sand. Binder properties were determined using scanning electron microscopy and energy dispersive X-ray. Meanwhile, the fresh properties (slump flow) and hardened properties were determined (compressive strength and mass density). In the hardened properties test, two types of curing were used: water and sealed curing.

The compressive strength of mortar decreased as the amount of bottom ash as cement replacement. However, the compressive strength increased when bottom ash was used as aggregate replacement. Additionally, bottom ash was sufficient as a substitute for fine aggregate than as a substitute for cement.

This research presents test results that are more straightforward to apply in the construction site.

One of the often-employed building constituents in the construction sector is concrete, which involves hydration of cement, leading to the generation of carbon footprints during its production. Also, massive amount of natural aggregate is illegally mined, which poses serious environmental issues along with ecological misbalance. Researchers are in continuous search of appropriate substitutes to mitigate those challenges and develop innovative concrete mix. Consequently, depletion of natural resources, the disturbances to the environmental and ecological imbalance will reduce. The purpose of this study is to develop a Portland Slag Cement based novel sustainable concrete incorporating Alccofine and Recycled Refractory Brick as fractional replacement of cement and fine aggregate, respectively and evaluate its destructive, non-destructive and microstructural properties.

M25 grade of concrete adopting 0.45 water-binder proportion, with diverse percentage of Alccofine as fractional substitution of cement and 20% of recycled refractory brick (RRB) as fine aggregate, has been cast and evaluated for diverse mechanical strength following a curing of 7, 14 and 28 days. Scanning electron microscopic analysis has been carried out to study the microstructural changes in the specimens.

Supplementary use of Alccofine enhanced normal compressive strength of sustainable concrete mix blended with Portland Slag Cement by a large amount at all levels of 7, 14 and 28 days of curing. Test results indicated development of a favourable high-strength sustainable concrete mix by substituting cement with Alccofine.

This manuscript has demonstrated the possibility of developing sustainable concrete blends by incorporating Alccofine 1203 and RRB as partial replacement of Portland Slag Cement and natural fine aggregate, respectively. The strength and potential of concrete incorporating RRB for wider and special application in adverse environmental conditions having higher thermal gradient, as RRB is a valuable waste from high temperature kiln and furnaces. Alccofine 1203 has been included in the concrete mix as an alternative to Portland Slag Cement to improve the mechanical strength properties and durability of concrete intended for adverse environmental application.