Strength Of Alkali Research Articles

Alkali-activated cements based on limestone-fly ash: Effect of the MgO-NaOH activation, compressive strength and reaction products

This study investigates the effects of alkaline activation with MgO-NaOH on the compressive strength and reaction products of alkali activated cements of limestone powder (PClz) and Class C fly ash (CV). Results showed that substitutions of 25%<PClz<75% allowed 25-76 MPa at 360 days of curing, obtaining the highest strength with 25%PClz-75%CV and 50%PClz-50%CV with 10 and 12% NaOH-MgO, respectively. The results suggest that PCLz participates in hydration reactions as filler and nucleating agent while CV is the main contributor to the advance of the chemical reactions. X-ray diffraction (XRD), Thermal analysis (TA) and Scanning Electron Microscopy (SEM) indicated the formation of M-S-H, and C, N-A-S-H-type products, in addition to carbonate phases such as hydrotalcite, gaylussite, and pirssonite. Traces of unreacted MgO were not observed indicating its whole incorporation into the reaction products.

Insight into the role of lanthanide metal oxides on the carbon deposition resistance of Ni/MSS catalysts for dry reforming of methane

Dry reforming of methane (DRM) can well convert CO2 and CH4 into syngas to further synthesize valuable chemicals, thereby realizing the resource utilization of greenhouse gases. However, the sintering and carbon deposition vulnerabilities of Ni-based dry reforming catalysts prevent them from being commercialized. The ethylene glycol impregnation method was used in this study to create a group of Ni/MSS catalysts added with lanthanide metal oxides (CeO2、La2O3、Sm2O3、Nd2O3). A range of characterization techniques were employed to examine the impact on the resistance to carbon deposition and sintering. Studies have shown that lanthanide metal oxides enhance the metal support interaction, promote active metal Ni dispersion and reduce Ni particle size. Meanwhile, the catalyst's alkali strength and basic site count both rise, and a large number of surface oxygen vacancies are produced, among which CeO2 has the most obvious effect. As a result, the catalyst's activity and resistance to carbon deposition and sintering are greatly increased, while also inhibiting the degree of graphitization of carbon deposition. According to the kinetic studies, the catalyst containing lanthanide metal oxides had an apparent activation energy for CH4 and CO2 that was lower than the Ni/MSS catalyst.

Improved strength of alkali activated materials based on construction and demolition waste with addition of rice husk ash

A promising solution to the environmental problem of managing a huge amount of construction and demolition waste (CDW) is its use as precursor in the production of new alkaline-activated cements. Specifically, the main objective of this investigation is to increase the strength of alkaline activated cements synthesized from unseparated CDW of low reactivity due to a high presence of crystalline phases in their composition. The effect of two factors is analyzed: the partial substitution of CDW by rice husk ash (RHA) (20–40 wt%) as well as the modulus of the alkaline activator used (Ms=SiO2/Na2O of 0.5, 1.0 and 2.0). Physical, mechanical and thermal testing, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) are used to characterize alkali-activated cements. Results show that the incorporation of increasing amounts of RHA and the increase in the modulus of the activator produce changes in the general structure of the gel, obtaining a greater amount of N-A-S-H geopolymeric gel with respect to the main reaction product, the C-A-S-H gel obtained in the control cements containing CDW as the only precursor. The new reaction products and the change in the microstructure make it possible to achieve a compressive strength of 59.6 MPa at 28 curing days in the materials with 40 wt% RHA and Ms= 2.0 compared to 18.5 MPa for the material developed exclusively from CDW. Therefore, this study validates the use of CDW together with RHA as precursors in the production of alkaline activated materials with improved technological properties. These green cements would help to reduce the presence of CDW and RHA in landfills and would generate new environmentally sustainable materials.

Investigating the strength and durability properties of alkali activated red mud for tailings pond embankment material

This article investigates the applicability of alkali-activated red mud (RM) as a geo-material for the construction of tailings pond (TP) embankments. A series of unconfined compressive strength (UCS) and direct shear tests (DST) are carried out to examine the mechanical performance of RM activated with sodium hydroxide (NaOH). While doing so, the influence of NaOH concentrations, curing conditions and curing period are also investigated. Furthermore, durability tests are performed to examine the weathering resistance of stabilized RM specimens against extreme environmental conditions. Finally, the effectiveness of alkali activated RM (as an embankment material) is demonstrated with the help of numerical analysis performed on a model TP. Based on the experimental results, the compressive strength of bare RM is improved from 0.34 MPa to 5.6 MPa, 0.57 MPa to 10.55 MPa and 0.97 MPa to 29.34 MPa under controlled ambient curing (CAC, 25±2 °C), open air curing (OAC, 25±7 °C) and dry curing (DC, 60 °C) conditions respectively. On the other hand, effective friction angle and cohesion of bare RM is found to increase from 16.76° to 52.85° and 6.58 kPa to 391.11 kPa respectively, after alkali activation. Furthermore, alkali activated RM specimens exhibit a significantly high weathering resistance than bare RM against 12 cycles of alternate wetting and drying. The numerical analysis reveals a notable increase in the factor of safety values when alkali activated RM is utilized for the construction of TP, indicating its potential as an embankment material.

Influence of bagasse ash powder and marble powder on strength and microstructure characteristics of alkali activated slag concrete cured at room temperature for rigid pavement application

In this research, an attempt is made to partially replace ground granulated blast furnace Slag (GGBS) with a binder rich in SiO2 and CaO in alkali activated slag concrete (AASC) to increase workability and setting time. GGBS is replaced with bagasse ash powder (BAP) in 5%, 10%, and 15% of the binary mix, and subsequently with marble powder (MP) in 5% and 10% of the binary mix. After establishing the best mix for both binder replacements, a ternary mix with 5% BAP and 10% MP is created. The fine aggregates used in the comparison are 100 % river sand and slag sand. 10 M sodium hydroxide and the alkaline to binder ratio is 0.4, were used. Mechanical properties such as compressive strength, split tensile strength, and flexural strength are performed cured at 1, 3, 7, and 28 days samples. To further understand the intrinsic mechanism of strength development, microstructure, morphology and mineralogy on AASC are investigated. Based on the findings, it can be inferred that AASC mixes have a higher strength than OPC mixes. The mechanical strengths of the AASC binary mix with 10% MP and 5% BAP are higher. The microstructural analysis reveals the mixes developed with BAP and 100 % GGBS, had a denser microstructure than the normal mixes. The mechanical properties obtained for most of the AASC mixes are significantly higher than the IRC SP:62-2014 recommendations for rigid pavements for low volume roads.

Shrinkage, compressive and bond strengths of alkali activated/cement powder for alternative coating applications

This paper reports the properties of a novel coating material produced from alkali-activated/cement powder (AACP), including setting time, strength development, drying and autogenous shrinkages, and bond strength of one-part AACP paste-coated reinforcing steel bars in concrete. The AACP paste was prepared by activating a mixture of dry geopolymer powder (GPP), Portland cement (PC), and silica fume (SF) with tap water and 2 M sodium hydroxide solution. The effect of PC replacement, sodium silicate-to-sodium hydroxide solution (SS-to-SH) ratio, and pre-curing temperature in the production of GPP on the properties of AACP paste were also investigated. Test results showed that the incorporation of FA and PC activated with an SS-to-SH ratio of 2.0 for the production of GPP decreased their setting time of fresh one-part AACP pastes, whereas their strength development marginally increased. Furthermore, the increasing PC content and SS-to-SH ratio had an adverse effect on drying and autogenous shrinkages. However, the pre-curing temperature had a marginal effect on their shrinkages. In addition, one-part AACP paste-coated reinforcing steel bars positively affected the bond strength of reinforced concrete, especially for the GPP produced by FA without PC. The increased reaction products at the contact zone could assist in improving their bond strength. It can be recommended that the use of FA without PC activated with a low SS-to-SH ratio in the production of GPP would be beneficial in improving shrinkage and bond strength while providing high equivalent substrate stiffness (ks).

Biocomposite optimization with NaOH-modified bagasse fiber, polybutylene succinate, and poly(lactic acid) using RSM approach

Alkali-treated bagasse fiber was used as a process variable for optimization of the properties of polybutylene succinate/poly(lactic acid)-based biocomposites using Box-Behnken design (BBD) and response surface methodology (RSM). The optimum conditions for three factors, i.e., NaOH-treated bagasse fiber (0.55 to 1.65 g), polybutylene succinate (1.1 to 2.3 g), and poly(lactic acid) (2.2 to 3.4 g) on the bending strength of biocomposite were investigated. The optimum combination was 0.91 g of NaOH-treated bagasse fiber, 1.14 g of polybutylene succinate, and 3.10 g of poly(lactic acid). The bending strength for NaOH-treated bagasse fiber/polybutylene succinate/ poly(lactic acid) composite was 27.0 MPa, which was 26.0% higher than native bagasse fiber-based composite. The composites were also characterized by thermogravimetric analysis, mechanical testing, Fourier transform infrared, scanning electron microscopy, water absorption, and contact angle tests. Results demonstrated that the bending strength, impact strength, and tensile strength of alkali treated bagasse fiber-based biocomposite increased by 26.0%, 15.5%, and 23.3%, separately, compared with native bagasse-based composite after sequential homogenization, compounding, and hot pressing. The hydrophobicity for alkali-treated bagasse fiber/PBS/PLA was also improved. Thus, NaOH-treated biomass materials/biodegradable polymer was judged to be suitable for preparing green composite materials.

Diversification of product-derived ionic liquids and application in DMC synthesis without introducing any impurities

Various strongly basic ionic liquids with distinctive structures, including single and double ended quaternary ammonium and phosphorus salts, were first synthesized based on hydroxyethoxy anion (HOCH2CH2O–) from the product ethylene glycol. Nature was characterized by NMR, FTIR, TG and acid-base titration. Its alkali strength was equivalent to that of sodium methoxide, demonstrating superior alkalinity. Influences of cation structures and C1-C4 alcohols structures on transesterification efficiency were investigated. Under mild conditions (68 °C for 5 min), DMC yield was 42.8% with a TOF value of 2853.6 h−1 when [TBAB]OCH2CH2OH as catalyst with only 0.18% EC molar content, indicating good catalytic performance. Comparison was made for reaction results between the synthesized catalysts and reported catalysts in literatures. The reaction mechanism was further deduced. Activation energies of positive and reverse reactions were determined as Ea+=32.0 kJ·mol−1 and Ea-=15.3 kJ·mol−1 through kinetics calculation. Relying on its decomposability and recyclability of decomposition products, a new catalyst circulation process without introducing any impurities was proposed and verified.

Chemical composition and physico-mechanical properties of carbonated alkali activated concrete and mortar

This paper investigates the influence of CO2 concentration (ambient and 5%) and duration of exposure on the carbonation, alkali content and pH of alkali activated concrete (AAC) and mortar produced from a ggbs based alkali activated cementitious material (AACM). Depth of carbonation was measured at regular intervals by the standard phenolphthalein indicator test method. The alkali content, mineralogy, and pH of the AAC in its carbonated and non-carbonated zones was determined by XRD, XRF, EDS and pH analysis. The effect of carbonation on physical properties (porosity, shrinkage) and mechanical properties (compressive strength) of alkali activated concrete (AAC) and mortar (AAM) together with their corresponding Portland cement-based specimens (PCC and PCM) was determined.The results show significantly high pH (between 10 and 10.5) at the carbonated zone of AAC and AAM. The high pH at the carbonated zone of AAC and AAM depicts sufficient alkalinity within the zone to prevent reinforcement corrosion due to carbonation. The alkalis Na+, K+, Al3+ and Mg2+ are more abundant in AAC and AAM which boost its alkalinity relative to the control PCC and PCM. The phenolphthalein test is more sensitive for detecting the carbonation of alkalis Ca(OH)2 and C–S–H which are predominant in PCC and PCM.The long-term depth of carbonation is lower in AAC than the control PCC under ambient CO2 exposure, but it is greater under accelerated carbonation (5% CO2) when kinetically unstable reactions occur, and bicarbonate is also formed. Results on the total drying and carbonation shrinkage, carbonation rate, and compressive strength are also reported which show the dominant influence of porosity of AAC and PCC.

Influence of RHA on strength and durability properties of alkali activated concrete

The ever-increasing demand from the building sectors drives the production of cement, which in turn leads to a rise in carbon dioxide emissions and contributes to the acceleration of global warming. To reduce the amount of cement that is used, an alternative binder made from agricultural and industrial waste products like rice husk ash (RHA) and ground granulated blast furnace slag (GGBS) among others, has been selected. Alkali activated concrete (AAC) is prepared by mixing binder, coarse aggregate, fine aggregate with an alkali activator. The impact of RHA substitution on workability, compressive strength and durability of GGBS based AAC is evaluated in this study. The slump value reduces as increase in the percent of RHA in AAC mix. The increase in curing time enhances the compressive strength of GGBS-RHA based AAC. The durability parameter as water absorption testing was performed after 28 and 90 days of curing, while depth of carbonation and H2SO4 attack were evaluated after 28 days of curing. As per the test results, adding more RHA up to 10% enhances the strength and durability of GGBS based AAC. Although the strength was reduced by utilizing more than 10% RHA in the AAC mix, but still the compressive strength more than 45 MPa is attainable. The water absorption and depth of carbonation both increases by using higher substitution of RHA in AAC mix. According to the H2SO4 attack test results, substituting RHA at a lower replacement level results in improved durability properties while raising the acid curing gradually reduces the strength of AAC.

Experimental studies on strength and durability of alkali activated slag and coal bottom ash based geopolymer concrete

This thesis work describes the experimental evaluation of the durability and strength properties of nominally mixed conventional concrete of grade M35, Alkali Activated Slag Based Geopolymer Concrete. Research on Rapid Chloride Permeability Test (RCPT) durability properties has been conducted. Sodium hydroxide (NaOH) and sodium Chloride (NaCl) must be mixed in a 2.5:1 M ratio and at molarities of 12 and 16, respectively, in order to make alkali activators, with dry curing and open-air curing serving as distinct curing regimes. NaOH concentrations of 12 M and 16 M were used to make nine distinct mixes, one of which was designated as the control mix. Then, these mixtures were cured at room temperature in the open air. Prior to the testing day, they were maintained at room temperature after a 24-hour dry curing procedure at 90 °C in a hot air oven. Each of the nine mixes underwent split tensile and flexural strength and durability testing after 90 days. Compressive strength tests are conducted at 28, 56, and 90 days. The results show that tensile strength increases as NaOH solution concentration decreases, but compressive and flexural strength increase as NaOH solution concentration increases. However, it was discovered that the Geopolymer concrete made from Alkali Activated Slag and Coal Bottom Ash (CBA) did not perform well in tests of water fast chloride penetrability because surface cracking predominated. When compared to the results of the control mix, the Alkali Activated Slag and Coal Bottom Ash (CBA)-based geopolymer concrete mix shows a superior improvement in strength measures than standard concrete. At this time, it seems that making geopolymer concrete costs less than regular concrete.

Performance evaluation of alkali activated slag based recycled aggregate pervious concrete

The present study attempts, a detailed evaluation of the strength performance of Alkali Activated Slag based Pervious Concrete (AASPC) mixes, containing fly ash and ground granulated blast furnace slag (GGBS) as binders. Fly ash and GGBS, by-product obtained from thermal power plants and steel industries respectively, is incorporated in the AASPC mixes as a full replacement to ordinary Portland cement (OPC). Initially OPC and AASPC mixes are designed to obtain M30 grade. OPC based pervious concrete is considered as control concrete. Pervious concrete is a type of concrete that has a high-water permeability and a higher void content than regular concrete.Experiments investigates the effect of the addition of Recycled Coarse Aggregate (RCA) on the physical and mechanical properties of alkali activated pervious concrete. Certain physical test has been conducted on recycled coarse aggregate to check the quality of aggregates, RCA varying percentage in 0, 25, 50, 75 and 100%, in the mixes. All mixes of alkali activated pervious concrete includes 50% of GGBS and 50% of fly ash from total binder content. Alkali activators used are, sodium hydroxide pellets and sodium silicate liquid. Workability of the alkali activated pervious concrete has a low slump value compare to the control concrete, but the workability of pervious concrete with cement is equal to alkali activated pervious concrete and workability will decreases with increase in RCA percentage because has a high capacity of water absorption. Compressive strength of alkali activated pervious concrete has increased by 23% compared to the OPC based pervious concrete and then there will be a decrease in compressive strength with increase in RCA percentage. The flexural strength and split tensile strength results for both the alkali activated pervious concrete and OPC based concrete shows almost similar values. Permeability and void ratio results shown increase with increase in RCA percentage in AASPC.

Enhanced enzymolysis and bioethanol yield from tobacco stem waste based on mild synergistic pretreatment

The use of mild pretreatment conditions can significantly lower the cost of the biorefining process. This study evaluated a mild pretreatment approach for tobacco stem waste using a combination of dilute acid and dilute alkali. By optimizing the pretreatment conditions, we obtained a high reducing sugar concentration at a pretreatment temperature <100°C. Increasing the acid or alkali strength in a single pretreatment step did not always improve the result; instead, the synergistic effect of both pretreatment components was important. To increase the bioethanol titer, a high solid loading, 30%, was used for bioethanol fermentation. Compared with batch fermentation, enzyme feeding with a shorter feeding period (24 h) enhanced the bioethanol production by 4.32%, generating 86.88 g/L bioethanol. The results provide valuable insights into the effects of two-step acid/alkali pretreatment on enzymolysis. The findings suggest that the optimized synergistic pretreatment process is efficient for bioethanol fermentation.

Effect of alkali and silane treatment on water absorption and mechanical properties of sisal fiber reinforced polyester composites

The present work deals with the effect of water absorption on the mechanical properties of untreated, 10% alkali-treated, and 10% alkali plus 1% silane treated sisal fibers (5%, 10%, and 15%) reinforced polyester composites. Hand lay-up was used to create the composite. The samples were prepared in accordance with ASTM standards, and tests for tensile strength, flexural strength, impact strength, and water absorption were performed. An increase in the tensile, flexural and impact strength was observed with an increase in fibre loading for untreated, alkali-treated and alkali plus silane treated sisal fibre reinforced polyester composites without water absorption, the increase being maximum for 10% alkali plus 1% silane treated fibre composite. Water absorption reduces tensile strength while increasing flexural and impact strength in untreated sisal fiber reinforced composites. There is an increase in tensile, flexural, and impact strength with higher fiber loading for 10% alkali-treated and 10% alkali-treated plus 1% silane treated sisal fiber reinforced polyester composites with and without water absorption. The tensile, flexural, and impact strength of alkali plus silane treated fiber is maximum at any given fiber loading, indicating that the alkali plus silane treatment is effective in improving the fiber matrix interface. Water absorption increases with fiber loading in untreated, 10% alkali-treated, and 10% alkali plus 1% silane treated sisal fiber reinforced polyester composites, with the rate being lowest in alkali plus silane treated fiber reinforced composites.

Experimental Research on Mechanical and Shrinkage Properties of Alkali Activated Low-Carbon Green Concrete.

This paper describes orthogonal experiments to investigat the effects of content of fly ash and slag, sol ratio, modulus of sodium silicate and expander on the compressive strength and shrinkage of alkali activated low-carbon green concrete (AAGC) of different ages. The microstructures and hydration product compositions of AAGC with different proportions were further studied by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Mercury Intrusion Porosimetry (MIP). The results show that with an increase of fly ash content, the compressive strength of AAGC gradually decreases, the decline of compressive strength at 28 d is smaller than that of 7 d, and the shrinkage strain gradually increases at 28 d. As the sol ratio increases, the compressive strength increases first and then decreases. When the sol ratio is 0.42, the compressive strength is maximal at 28 d; the same is true for compressive strength at 7 d. Additionally, an increase of sol ratio can reduce the shrinkage strain at 28 d. Finally, when the sol ratio was 0.46, the shrinkage decreased by 30.5% compared with 0.40 at 28 d. As the modulus of sodium silicate (Ms) increases, the compressive strength first increases and then decreases. When Ms is 1.4, the compressive strength reaches the maximum. As Ms increases, the shrinkage strain decreases first and then increases at 28 d. When Ms is 1.0, the shrinkage strain is the maximum at 28 d. Finally, with an increase in the content of expander, the compressive strength decreases at 7 d and 28 d, and the shrinkage strain decreases at 28 d. The shrinkage strain at 28 d is the minimum with 9% content. AAGC mixed with a small amount of fly ash and expander has more hydration products and significantly reduced cracks. In addition, the proportion of small hole volume of AAGC increases, while the proportion of large hole volume decreases. AAGC mixed with fly ash and slag without expander has more unhydrated particles and its structure is loose.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

In the context of a carbon–neutral era, conversion of greenhouse gas CO2via chemical catalysis is a powerful means. Using CO2and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca12Al14O33crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63 % conversion and 100 % selectivity). The special crystal phase structure of Ca12Al14O33remains stable at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H2O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

Effect of Water Absorption on the Mechanical Properties of Wheat Straw Fibre Reinforced Polystyrene Composites

The present work deals with the effect of water absorption on the mechanical properties of alkali plus silane treated wheat straw reinforced polystyrene composites. Wheat straw polystyrene composite was prepared with different fibre loading (5%, 10%, 15%, 20%, 25%) by compounding process using twin screw extruder. Samples were prepared by the compression moulding process. There was a decrease in the tensile strength initially at 5% fibre loading followed by an increase in it with higher fibre loading. There is an increase in flexural strength up to 15% fibre loading followed by decrease in it with higher fibre loading. There is an increase in the hardness initially at 5% fibre loading followed by decrease in it with higher fibre loading. There is an increase in water absorption with percentage increase in fibre loading. Tensile strength, flexural strength, and hardness of alkali plus silane treated wheat straw reinforced polystyrene composites with water absorption is always less than alkali plus silane treated wheat straw reinforced polystyrene composites without water absorption.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

<h2>Abstract</h2> In the context of a carbon-neutral era, conversion of greenhouse gas CO₂ via chemical catalysis is a powerful means. Using CO₂ and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca₁₂Al₁₄O₃₃ crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63% conversion and 100% selectivity). The special crystal phase structure of Ca₁₂Al₁₄O₃₃ maintains stability at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H₂O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

Effects of sodium chloride on the mechanical strength of alkali activated volcanic ash and slag pastes under room and elevated temperatures

This study investigated effects of the sodium chloride on the microstructural and mechanical properties of alkali activated volcanic ash (VA) and ground granulated blast furnace slag as well as Portland cement pastes. To this end, unconfined compressive strength (UCS), scanning electron microscopy (SEM)-EDS-Mapping, FTIR, and XRD tests were conducted. Furthermore, effects of curing temperature on the binding capacity of chloride in alkali activated cements were examined in both elevated (HT) and room (RT) temperature conditions. The VA was replaced by slag at 0, 50, and 100 wt%. Based on the results, samples containing 100 wt% slag showed the highest mechanical strength in both curing conditions. Besides, addition of sodium chloride from 0 to 10 wt% did not significantly affect the strength of samples containing 100 wt% volcanic ash in both curing conditions. On the other hand, in HT condition, mechanical strength of samples containing 50 and 100 wt% slag, as well as Portland cement pastes increased with increasing sodium chloride from 0 to 2.5 wt%, and further addition of sodium chloride by up to 10 wt% led to a reduction in their strength. However, compressive strength of samples containing 50 and 100 wt% slag, as well as Portland cement samples, decreased with the addition of sodium chloride from 0 to 10 wt% in RT condition. Microstructural investigations were conducted, aiming to find the mechanism controlling the reactions. It was found that (N,C)-A-S-H and C-S-H gels were the dominant factor in the solidification and encapsulation of chloride ions in slag-based samples.

Bond Strength and Fracture Toughness of Alkali Activated Self-Compacting Concrete Incorporating Metakaolin or Nanosilica

This study aims to evaluate the effect of nanosilica (NS) and metakaolin (MK) as binder replacement materials on the fresh and hardened characteristics of slag (GGBS)-based alkali-activated self-compacting concretes (A-ASCC). Therefore, nine A-ASCC mixes, with and without metakaolin, were prepared, as well as mixes with and without NS incorporation. In the production of A-ASCC mixes, GGBS was used as a binder material. The fresh properties of A-ASCC were determined using the L-box, V-funnel, T50 value, and slump flow tests, while the hardened properties were examined using compressive strength, bonding strength (pullout test), fracture toughness, and flexural tensile strength tests. A relationship analysis was also conducted on the A-ASCC experimental data. The experimental results showed that NS and MK had a negative effect on the fresh properties of GGBS-based A-ASCC mixtures, whereas metakaolin had a greater influence. The addition of 1% and 2% NS, on the other hand, improved the mechanical performance of the A-ASCC specimens significantly. The use of more than 2% NS had a harmful effect on the mechanical properties of A-ASCC. A 5% replacement ratio of metakaolin improved the mechanical properties of A-ASCC. The use of metakaolin at ratios of more than 5% had a negative effect on the properties of A-ASCC.