► Activation of slag by liquid sodium silicate produced rapid set and high shrinkage. ► Strengths of AAS mortars increased with an increase in the activator Na dosage. ► Sensitivity of AAS mortars to ...dry curing conditions was higher than OPC mortars. ► SSRe and especially SHR chemical admixtures reduced the shrinkage of AAS mortars. ► SSRe admixture had no impact on carbonation while SHR admixture had little effect.
This paper presents the influence of shrinkage-reducing (SHR) and superplasticizing and set-retarding admixtures (SSRe) on the properties of slag pastes and mortars activated by liquid sodium silicate with different dosage and modulus ratio. Properties in the fresh and hardened state for these binders were investigated by means of measuring some properties including setting time, flowability, flexural strength, compressive strength, carbonation and shrinkage. In this study, fifteen pastes and mortars were prepared. Liquid sodium silicate was used to activate the slag at two sodium concentrations, 4% and 6% by mass of slag. Liquid sodium silicate and sodium hydroxide were blended to obtain 0.75 and 1 modulus ratio of SiO2/Na2O. Results showed that although the higher percentage of sodium in the activator produced a higher strength, workability and setting times rapidly decreased with the higher sodium concentration due to instantaneous reaction and quick hardening of slag activated by liquid sodium silicate. None of the admixtures generally had an impact on the setting times of alkali-activated slag (AAS) pastes. SSRe admixture increased the flow rate of AAS mortars while SHR admixture partially affected the flow values of AAS mortars. SHR admixture exhibited a slight decrease in the carbonation depths of AAS mortars. SSRe and particularly SHR chemical admixtures reduced the shrinkage of AAS mortars. However, the shrinkage values of AAS mortars still were higher than those of ordinary Portland cement (NPC) mortars. Curing conditions had a significant effect on the mechanical behavior in the hardened state of AAS mortars compared to NPC mortars.
Since alkali activators negatively effect the environmental impact assessment, it is necessary to develop the alternative activators from natural sources with low environmental impact. Therefore, in ...this study, the usage of boron refined products colemanite, ulexite and boron pentahydrate as activators in slag-based alkali-activated mortar systems was investigated in detail. Flexural and compressive strength tests, isothermal calorimetry measurement, thermogravimetric and differential thermal analysis, inductively coupled plasma mass spectrometry analysis, field emission scanning electron microscopy, and energy dispersive analysis and elemental mapping and X-ray diffraction analysis were carried out on the samples. In addition, sample production was subjected to life cycle analysis (LCA) with a cradle-to-gate approach using two different transportation scenarios. According to the results obtained, it was determined that colemanite, ulexite and boron penta hydrate, when used in optimum proportions, had a positive effect on strength (up to increase 40% compressive strength by 20% ulexite replacement) and could be used as an activator in slag-based alkali-activated systems. The positive results obtained in strength as a result of using boron-refined products are also supported by other test results conducted within the scope of the study. Furthermore, according to the LCA results, it was observed that there was a significant decrease in global warming potential with the substitution of 20% colemanite, ulexite or boron pentahydrate as activators, not only compared to the reference sample but also traditional cementitious systems.
•Replacing boron product with alkali activator result with increase in strengths.•Boron products caused lower heat flow peaks and the total heat of hydration.•Boron products provide compact and denser microstructure compare to reference.•Boron products shows better environmental performance than reference mortar.
In this work, the utilization of shredded waste Poly-ethylene Terephthalate (PET) bottle granules as a lightweight aggregate in mortar was investigated. Investigation was carried out on two groups of ...mortar samples, one made with only PET aggregates and, second made with PET and sand aggregates together. Additionally, blast-furnace slag was also used as the replacement of cement on mass basis at the replacement ratio of 50% to reduce the amount of cement used and provide savings. The water–binder (w/b) ratio and PET–binder (PET/b) ratio used in the mixtures were 0.45 and 0.50, respectively. The size of shredded PET granules used in the preparation of mortar mixtures were between 0 and 4
mm. The results of the laboratory study and testing carried out showed that mortar containing only PET aggregate, mortar containing PET and sand aggregate, and mortars modified with slag as cement replacement can be drop into structural lightweight concrete category in terms of unit weight and strength properties. Therefore, it was concluded that there is a potential for the use of shredded waste PET granules as aggregate in the production of structural lightweight concrete. The use of shredded waste PET granules due to its low unit weight reduces the unit weight of concrete which results in a reduction in the death weight of a structural concrete member of a building. Reduction in the death weight of a building will help to reduce the seismic risk of the building since the earthquake forces linearly dependant on the dead-weight. Furthermore, it was also concluded that the use of industrial wastes such as PET granules and blast-furnace slag in concrete provides some advantages, i.e., reduction in the use of natural resources, disposal of wastes, prevention of environmental pollution, and energy saving.
There are very few studies in the literature on the usage of CKD in cementitious systems. This article presents the laboratory study results on the influence of cement kiln dust (CKD) on the ...properties of mortar made with cement kiln dust and Portland cement. The article aims to prevent CKD’s (known as a hazardous waste product) damage to nature by utilizing CKD in cementitious systems and contributing to sustainability by reducing cement amount in the cementitious system. For this purpose, 5%, 10%, 15%, and 20% of CKD were replaced with cement and binary cementitious systems were formed. For all mortar mixes, the water/binder ratio was kept constant at 0.5, and the sand/binder ratio was 3. Workability, dry unit weight, water absorption ratio and porosity, flexural strength, compressive strength, abrasion, carbonation, and high-temperature resistance tests were performed on the mortar specimens. Based on the results of laboratory work, it was observed that the replacement of CKD with cement reduces the workability of fresh mortar. Compressive and flexural strengths of CKD-added mixtures were found to be equivalent or insignificantly lower than that of the control sample. The addition of CKD had a negligible effect on water absorption and porosity of samples. Besides, the residual compressive strength determined after the elevated temperature test for the sample made with CKD were found to be equivalent or higher compared to the control sample. Present laboratory studies showed that utilization of CKD in cementitious mortar system is feasible in terms of testing conducted.
This paper reports an experimental study of the influence of elevated temperature on alkali activated slag (AAS) and slag‐metakaolin (MK) systems. The residual compressive and flexural tensile ...strengths, ultrasonic pulse velocity (UPV) and porosity and water absorption ratios of AAS and AAS‐MK composites after subjected to elevated temperatures of 200, 400, 600, 800, and 1000°C were investigated. Two different procedures were applied for cooling the specimens. The changes in the microstructure of the composites after subjected to high temperature were examined with scanning electron microscope and X‐ray diffraction. Test results reveal that depending on the increasing temperature, the residual compressive strength, flexural tensile strength, and UPV values of the specimens decreased, and porosity and water absorption ratios increased. The minimum strength results of AAS and AAS‐MK specimens were observed at 800 and 600°C, respectively. In particular, there have been significant changes in the internal structure of AAS and AAS‐MK specimens exposed to 1000°C and new reaction products were observed. Test results have shown that AAS specimens are a new alternative that can be developed for use in environments exposed to high temperatures. Since this new composite contains only slag binder and slag aggregate, it can be an economical product that use fully recycled material and these properties can increase the application areas of environmentally friendly material.
This paper shows results of laboratory study on the effects of nano-SiO2 on Portland cement-fly ash systems. It is aimed to improve performance of fly ash–cement systems, particularly at early age, ...with the inclusion of nano-SiO2. In order to observe the effects of nano-SiO2 particles on the strength and hydration kinetics of fly ash blended cementitious systems, binary and ternary systems were prepared by adding 0.25–1.5% nano-SiO2 by weight of blended cements. Workability, setting time, water absorption capacity, fire resistance, compressive strength and isothermal calorimeter tests were conducted on the cementitious systems. The results indicate that increasing quantity of fly ash increased workability, setting time, water absorption capacity of cementitious systems, whereas the increasing quantity of nano-SiO2 reduced these values. Significant increment in compressive strength were observed, especially at early ages of fly ash–cement systems with nano-SiO2 addition, compared to fly ash added systems, which may compensate for the decrease in compressive strength caused by fly ash. Nano-SiO2 addition accelerated hydration reactions at early age. By partially eliminating the negative effects of fly ash with nano-SiO2, high rates of fly ash can be used in cementitious systems, thus forming more sustainable systems.
In this study, the influence of a pre-rest period before heat curing (as a new parameter), on the physical properties, flexural and compressive strength, and microstructure of geopolymer mortars and ...pastes produced with alkali activation of fly ash were investigated. In this context, geopolymer mortar and paste samples were prepared and pre-rested under laboratory conditions for 0, 1, 2, 3, 7, 14, and 28 days before heat curing. After the pre-rest period, the samples were subjected to heat curing at 75 °C in an oven, for 2 days. Mortar and paste samples exposed to a pre-rest period while in the fresh state before heat curing were compared with control samples without pre-resting. Water absorption, porosity, specific gravity, capillarity, flexural strength, compressive strength, and abrasion resistance tests were conducted on the geopolymer mortar samples. A reaction kinetics study using an isothermal calorimeter, XRD, and SEM analyses were performed on the geopolymer paste samples for microstructural investigations. Based on the results obtained, it was observed that the mechanical strength of the samples subjected to the pre-rest period before heat curing increased considerably compared to the reference (without pre-resting) samples. In addition, because of pre-resting, the capillarity coefficient, water permeability, and porosity of the samples decreased compared to the reference samples, and it was concluded that pre-resting improves durability-related properties. Moreover, the reaction kinetics and SEM analysis results, supporting the above findings, showed that a pre-resting period increases the geopolymeric reaction products and causes a denser microstructure.
•Influence of applying pre-rest period before heat curing on the properties of fly ash based geopolymer was evaluated.•Pre-rest period enhanced and improved mechanical and durability related properties of fly ash based geopolymer.•The pre-rest period, allowing more time for ion transfer resulted with a more compact and denser microstructure.•Isothermal studies proved the pre-rest periods contributes to the geopolymeric reaction.
This research shows the results and conclusions of an experimental study that aims to shed light on the mechanical performance of Slurry Infiltrated Fiber Concrete (SIFCON) (i.e. compressive ...strength, splitting tensile strength, flexural strength, Poisson's ratio, elastic modulus, and ultrasonic pulse velocity (UPV) and explore its efficiency at elevated temperature (i.e. 200, 400 and 600 °C) with different steel fiber ratios of 5 %, 7.5 %, and 10 % cured standard and in boiling water (accelerated curing). Hence, sets of cylinders and prisms are cast and tested under ASTM standard conditions. The results indicate that mechanical properties improve by increasing the steel fiber ratio up to 7.5 % in the case of a standard curing system, but more improvement is achieved with a steel fiber ratio up to 10 % in case of accelerated curing with boiling water. Also, the results indicate the superiority of the accelerated curing method for flexural and splitting tensile strength. Fly ash has a good contribution to the enhancement of mechanical performance of SIFCON with high steel fiber ratios. A decreasing and drastic reduction in compressive strength with increasing temperature above 200 and 400 °C for control specimens and SIFCON specimens with fiber ratios of 5 %, respectively are observed. While a dramatic gain in the strength of SIFCON samples with fiber ratios of 7.5 % and 10 % is concluded. High ratios of steel fiber can retard the spalling of concrete; hence it makes SIFCON the unique material for resisting explosive loads.
Abstract The demand for cement usage increases in the world, currently. It is known that using industrial waste materials in concrete as cement or aggregate replacement as part of waste management as ...well as conserving natural resources is getting wider. Due to these facts, in this work, an investigation was carried out on the utilization of waste marble powders as cement replacement mineral materials. In this context, marble powder replaced cement at 5%, 10%, 15% and 20% in mass basis, and mortars were produced. In mortar mixtures, water-binder ratio was chosen as 0.5, and sand-binder ratio was taken as 3. Workability of fresh mortar was measured. Unit weight, water absorption, and porosity, compressive and flexural strengths, abrasion, carbonation and drying shrinkage measurements testing were carried out on hardened mortar specimens. Influence of elevated temperature on hardened mortar mixture was also investigated. As a result of laboratory study, it is concluded that replacing marble powder with cement result with a favourable contribution to workability of fresh mortar, as well as resistance to elevated temperature. It also reduced drying shrinkage of mortar in comparison to reference mortar made without marble powder. However, it influenced water absorption, abrasion, and carbonation resistance of mortar, unfavourably. For short term curing duration, replacement of marble powder with cement reduced compressive strength insignificantly for 5% and 10% marble powder replacement, but, reduced it significantly for 15% and 20%. However, at long term curing at 90 days, the difference between strength of reference mortar and marble containing mortar was diminished, particularly for mortar containing 5% and 10% marble powder.
This paper reports a part of an ongoing laboratory investigation in which the compressive strength of ground granulated blast-furnace slag (GGBFS) concrete studied under dry and wet curing ...conditions. In the study, a total of 45 concretes, including control normal Portland cement (NPC) concrete and GGBFS concrete, were produced with three different water-cement ratios (0.3, 0.4, 0.5), three different cement dosages (350, 400, 450
kg/m
3) and four partial GGBFS replacement ratios (20%, 40%, 60%, 80%). A hyperplasticizer was used in concrete at various quantities to provide and keep a constant workability. Twelve cubic samples produced from fresh concrete were de-moulded after a day, then, six cubic samples were cured at 22±2
°C with 65% relative humidity (RH), and the remaining six cubic samples were cured at 22±2
°C with 100%RH until the samples were used for compressive strength measurement at 28 days and three months. Three cubic samples were used for each age and curing conditions. The comparison was made on the basis of compressive strength between GGBFS concrete and NPC concrete. GGBFS concretes were also compared within themselves. The comparisons showed that compressive strength of GGBFS concrete cured at 65%RH was influenced more than that of NPC concrete. It was found that the compressive strength of GGBFS concrete cured at 65%RH was, at average, 15% lower than that of GGBFS concrete cured at 100%RH. The increase in the water-cementitious materials ratios makes the concrete more sensitive to dry curing condition. The influence of dry curing conditions on GGBFS concrete was marked as the replacement ratio of GGBFS increased.
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