Significant Reduction In Compressive Strength Research Articles

Advancing reinforcement of sustainable gypsum composites: High-performance design by reusing waste materials

This study tends to optimize and develop an innovative gypsum material by incorporating hybrid waste compounds. Using a Doehlert design, this work explores the effects of introducing paper (X1), polystyrene (X2), and polyester fibers (X3), as well as their interactions, on gypsum's thermophysical and mechanical behavior. Bulk density, thermal conductivity, flexural strength, compressive strength, and the fire resistance test were performed on the developed formulations. Statistical analysis emphasizes the significant influence of all process variables on gypsum properties. Polyester fibers notably enhance flexural strength when combined with the cooperative effect of paper and polystyrene wastes, which strike a balance between physical and mechanical characteristics. The optimum formulation parameters lead to a significant 33% decrease in bulk density, a 43% reduction in thermal conductivity, a notable 42% increase in flexural strength, and a significant reduction in compressive strength of around 50%, but still meet the 2 MPa standard. The new samples show ductile behavior, highlighting gypsum's potential as a load-bearing material with excellent thermal insulation properties and impressive fire resistance. This research significantly improves our understanding of the effectiveness of a gypsum compound incorporating waste in a hybrid manner, bringing this approach into line with sustainable development objectives.

Investigation on Effects and Properties of Concrete Structure after Exposed to Fire

Abstract: The integrity and strength of the materials used in reinforced concrete structures are highly influenced by their exposure environment. Exposing the building materials to high temperature changes their performance. The change in the performance is a result of the change in the material properties. When subjecting a building material to fire, the occurring damage depends on the severity of the fire in terms ofthe fire temperature and time of exposure. This study investigates the effects of fireexposure on the set of RC beams. Through controlled experiments, varyingtemperatures from 3000C to 7000C areapplied to RC beams, analyzing changes in compressive strength, spalling, andmicrostructure by using rebound hammer,UPV meter and applying two-point loading in UTM. Results indicate a significantreduction in compressive strength with increasing fire temperature, attributed to thermal degradation of cement paste and aggregate. Additionally, changes inmicrostructure, such as pore structure alterations and formation of cracks, are observed. Also, few of RC beams were strengthened using GFRP sheets as a U- shaped wrapping to entire beam and U- shaped wrapping at certain intervals. The strengthened specimens are again tested in UTM for two-point loading, the results of the tests showed the feasibility of rehabilitating RC beams exposed to fire using GFRP plates.U-shaped wrapping to entire beam showed the good performance

Compressive failure analysis of composite honeycomb sandwich panels with impact damage and stepped-scarf repairs

Composite honeycomb sandwich panels (CHSPs) have been widely used in the aerospace industry owing to their lightweight and superior mechanical properties. However, these CHSPs are susceptible to impact damage, leading to a significant reduction in compressive strength and potentially jeopardize aircraft safety. It is crucial to investigate repair methods for CHSPs with impact damage. This paper aims to evaluate the repair performance of CHSPs with impact damage through an analysis of their compressive failure behaviors. To accomplish this, both experimental tests and advanced numerical models are employed. The numerical models for the intact, damaged and stepped-scarf repaired CHSPs are established using the progressive failure analysis model, cohesive zone model and sandwich plate theory. A good agreement is observed between the experimental results and numerical predictions of compressive failure behaviors. Moreover, the validated numerical models are successfully utilized for determining optimum repair parameters by parametric analysis of the repaired CHSPs. The establishment of these numerical models offers an accurate and cost-effective evaluation of repair performance for CHSPs with impact damage, highlighting the novelty and main contribution of this paper.

Valorisation of municipal solid waste incinerator bottom ash for the production of compressed stabilised earth blocks

This research centres its attention on the valorisation of incinerator bottom ash derived from municipal solid waste with the aim of producing compressed stabilised earth blocks. Compressed stabilised earth blocks is prepared with 6–12% cement and 10–40% MSWIBA, whose performance is assessed in terms of strength and durability. This includes several properties of compressed stabilised earth blocks, including dry compressive strength, flexural strength, tensile strength, water absorption, wetting-drying cycle, ultrasonic pulse velocity and acid attack. The findings indicate that the inclusion of municipal solid waste incinerator bottom ash as a 20% replacement of soil enhances the compressive strength and ultrasonic pulse velocity of the blocks. Nevertheless, the excessive use of municipal solid waste incinerator bottom ash (beyond 20%) results in an augment of void content and a reduction in compressive strength. The results of the study suggest that the usage of municipal solid waste incinerator bottom ash in the blocks leads to the enhancement of their aesthetic qualities. The study employing scanning electron microscopy indicates an excessive quantity of ettringite crystals in the samples derived from ash of quantity beyond 20%. This is because these samples have higher porosity, which enables the acidic medium to penetrate samples easily and react with the cement hydration products. Hence, though showing less discolouration on the surface, these samples show a significant reduction of compressive strength at the end of the testing regime. Similar results were obtained for the wetting and drying test as well. Therefore, this study recommends a maximum usage of 20% municipal solid waste incinerator bottom ash as a replacement for soil.

Cow dung ash (CDA): A sustainable conductive filler for enhancing electromagnetic shielding property of cement mortar

Cow Dung ash (CDA) is a wide spread farm by-product, generated by burning dry cow-dung. Cement mortar, the work horse of construction industry inherently possesses significant electrical conductivity, thereby providing considerable electromagnetic shielding property. CDA is investigated as novel sustainable conductive filler, as sand replacement, for enhancing electromagnetic shielding property of cement mortar. The electromagnetic properties of CDA are determined employing standard wave guide techniques, in X band, and electrical conductivity around 10-2 S/m is observed. The electrical loss tangent is observed around 0.2–0.3. Cement mortar slabs with CDA as sand replacement are prototyped. Sand replacement till 15 % by volume is investigated. Considerable reduction in compressive strength is reported in literature for sand replacement beyond 15 %. After 28 days of curing, the prototyped slabs are subjected to electromagnetic shielding effectiveness determination, as per ASTM 4935 two antenna standard, in the X band of frequencies centred around 10 GHz. Shielding Effectiveness (SE) around 7 dB is observed for 3 % CDA as sand replacement, around 10 dB for 10 % replacement, and around 20 dB for 15 % CDA. Compressive strength measurement employing Universal Testing machine presented significant reduction in compressive strength as CDA replacement tend towards 15 %. Employing CDA loaded cement mortar for plastering, is a low cost, easy deployable solution for realizing customized electromagnetic shielding levels in buildings housing critical electrical and electronic infrastructure including servers and data centres. Realizing low cost, easy deployable customized shielding solutions is an upcoming research domain, primarily due to the anticipated increase in ambient electromagnetic field levels in our surroundings caused by the rampant deployment of communication technologies including 5G and IoT. Apart from providing positive environmental impact, acting as sand replacement, enhanced CDA utilization by engineering sectors can lead to good revenue generation model for rural economic development.

Improvement of the thermal properties of alkali-activated fly ash after high temperature by the Fe-based solid wastes

Compared with Portland cement, AAM was selected as the high-temperature resistant material. But there is still a trend toward a significant reduction in compressive strength at 600 ℃ and 800 ℃. Thus, in this paper, the Fe-based solid wastes, i.e., copper slag and iron tailing, were used to improve the compressive properties of fly ash-based AAM after high temperatures. The result shows that the residual compressive strength of the Fe-based solid waste samples is higher than that of the blank sample. The residual compressive strength increases by about 20 % at 800 ℃. Though the results of SEM-EDS, MIP, and XPS experiments, the mechanism of the effect of Fe-based solid wastes on the AAM could be summarized as follows: the iron element in the Fe-based solid waste samples is more concentrated after high temperature, which may be caused by the melting of the original iron mineral phase into a new mineral phase, filling the crack gap. And the formation of the Fe-O-Si amorphous phase would improve the densification of samples, resulting in the improvement of compressive strength.

Behavior of unconfined and polyethylene terephthalate (PET) FRP-confined coal reject concrete under compression

Fiber-reinforced polymer (FRP) confinement has been proposed to mitigate the detrimental effects of coal rejects concrete (CRC) in the present study. Polyethylene terephthalate (PET) FRP jacket was adopted to confine CRC as a new type of novel column members, which are referred to as PET FRP-confined coal reject columns (PFCCRs). PFCCRs are often sustainable and cost-effective structural columns as the PET FRP composites are generally made from recyclable PET waste and coal rejects are industry by-products. A total of 49 columnar specimens, consisting of 21 CRC specimens and 28 PFCCR specimens were tested under uni-axial compression to understand the mechanical behavior of unconfined and PET FRP-confined CRC. The main parameters evaluated in this study were the volume replacement ratio of coal rejects and the FRP thickness. The test results indicated that the unconfined CRC specimens exhibited a significant reduction in compressive strength with the increase in replacement ratio, whereas the ultimate axial strain was enhanced. Compared with plain CRC specimens, PFCCRs had excellent deformation capacity and compressive strength with a strain hardening stress-strain response. The maximum normalized ultimate axial strain and axial stress of most of the PFCCR specimens are over 30 and 7, respectively. The stress reduction segment will occur only when the FRP confinement is insufficient. Furthermore, the test results were compared with the predictions by using existing analysis-oriented and design-oriented models for LRS FRP-confined concrete to verify their accuracy.

Synergic effect between two pozzolans: Clinoptilolite and silica gel by-product in a ternary blend of a Portland cement system

Two types of SCMs such as clinoptilolite and silicagel by-product was incorporated in the OPC system and acted as pozzolanic materials. The individual effect of silicagel by-product led to the significant reduction of compressive strength due to soluble barrier layers made of CaF2 formed on the particles of OPC. In a ternary blend of a Portland cement system the synergetic effect of clinoptilolite and silicagel by-product led to the similar strength properties of hardened cement paste. Clinoptilolite acted as sorbent which sorb acidic fluoride ion impurities of silicagel by-product. This paper demonstrates the potential application of silicagel by-product and clinoptilolite as SCMs in the production of eco-friendly blended cements.

Investigation of Concrete Shrinkage Reducing Additives.

This paper analyzes the efficiency of shrinkage reducing additives for the shrinkage deformations of ordinary Portland cement (OPC) concrete and its mechanical properties. OPC concrete was modified with an organic compound-based shrinkage reducing additive (SRA), quicklime, polypropylene fiber, and hemp fiber. It was found that a combination of 2.5% quicklime and 1.5% SRA led to the highest reduction in shrinkage deformations in concrete, and the values of shrinkage reached up to 40.0%. On the contrary, compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. Hemp fiber did not show a significant shrinkage reduction, but it is an environmentally friendly additive, which can improve OPC concrete flexural strength. Polypropylene fiber can be used in conjunction with shrinkage reducing additives to improve other mechanical properties of concrete. It was observed that 3.0 kg/m3 of polypropylene fiber in concrete could increase flexural strength by 11.7%. Moreover, before degradation, concrete with polypropylene fiber shows high fracture energy and decent residual strength of 1.9 MPa when a 3.5 mm crack appears. The tests showed a compressive strength decrease in all compositions with shrinkage reducing additives and its combinations after 28 days of hardening.

The effect of using recycled PET aggregates on mechanical and durability properties of 3D printed mortar

3D concrete printing technology of cementitious materials is challenging in many aspects. Despite the workability and mechanical properties of a mix and hardened concrete or mortar, the researchers need to face problems with environmental impact and durability of printed elements. Furthermore, today thousands of tons of waste are produced and natural aggregates which are most used resources by volume in the construction sector are on the verge of exhaustion. To date, limited knowledge about utilized of artificial aggregate (including Polyethylene terephthalate (PET) in 3D printed mortar is available. The main objective of this study is to develop 3D printed mortar with PET granules as the replacement of natural aggregate (10 vol-% to 50 vol-%). The paper contributes to knowledge of properties of 3D printed composites with plastic aggregate. Four printable mixes were made: one reference mix and three mixes in which natural aggregate was replaced by PET granulate in quantities amounting to 10%, 30% and 50% (by volume), respectively. The replacement ratios were chosen on the base of literature review for ordinary cementitious mortars. Several strength tests were carried out for standard and printed specimens. In addition, a freeze–thaw resistance test and high temperature performance test were conducted to evaluate to validate the properties of artificial aggregate. The results show that PET granulate is useful in 3D printing owing to their buildability and extrudability properties. Furthermore, printed mixes with high amount of PET (30% and 50%) granulate shows high decreases in strength (up to 75%). Unfortunately, after the freeze–thaw resistance test specimens with a high amount of PET granulate (30% and 50%) indicated high strength reduction (up to 80%). Exposure to a temperature exceeding the melting point of PET results in significant reduction of compressive strength for printed specimens (up to 68.8 % for 50 % PET addition). In addition, mixes with up to 10% PET can be used for most structural elements even under varying thermal conditions (even under extreme cold temperature).

Compressive Strength Evaluation of Concrete with Palm Tree Ash

Concrete industry produces high carbon dioxide emissions that are harmful to the environment. As cement is the primary artificial component of concrete, most of the past studies focused on reducing the cement content in concrete manufacturing. To enhance the sustainability of concrete production, generally, cement is partially replaced with waste materials with similar characteristics such as silica fume and fly ash. One of the sources of such waste materials in date-producing countries is palm trees since each palm tree produces approximately 23 kg of waste annually. Currently, very limited use of palm tree waste exists in the concrete industry; specifically, palm tree leaves ash (PTA). This study is intending to evaluate the potential of adding PTA to concrete as a cement replacement by evaluating the compressive strength of PTA concrete. Several concrete cylindrical specimens were cast with variable percentages of added PTA. Three dosages of PTA (5%, 10%, and 15%) were added to the concrete as a substitute for cement by weight. The palm tree ash added to concrete was collected from burned palm tree branches and filtered based on its fineness. Assessment of the compressive strength of PTA-based concrete was performed at ages of 7, 28, and 56 days. The results of evaluating the compressive strength of the specimens showed that the concrete mixed with only 5% PTA possesses around 12% higher compressive strength than that without PTA. Further, increasing the dosage of added PTA to concrete yielded unfavorable results in terms of increasing the compressive strength. The addition of more than 10% of PTA to concrete as a replacement for cement triggered a significant reduction in compressive strength of the concrete. The findings of this study encourage partial replacement of cement with PTA in concrete up to 5% to reduce concrete carbon footprint and enhance sustainability of concrete manufacturing process with maintaining desired mechanical properties.

High-Temperature Behavior of CaO-FeOx-Al2O3-SiO2-Rich Alkali Activated Materials

Alkali-activated materials (AAMs) provide an opportunity to up-cycle several residues into added-value materials. Although generally praised for their performance under thermal loads, the thermal behavior of AAMs is dictated by a multitude of factors and the performance of CaO-FeOx-rich systems may differ from geopolymers. Therefore, this work ascertains the high‑temperature resistance of CaO‑FeOx-Al2O3-SiO2-rich AAMs. Mortars were exposed to different heating rates (≤10 °C/min) and temperatures (≤1100 °C), and volume and mass loss, apparent density, compressive strength (CS), mineralogical composition, and morphology were evaluated. At low heating rates, the main effects noted were densification and a gradual lightening of color as the temperature rose. CS underwent an abrupt decline at 750 °C and recovered at higher temperatures, reaching a maximum value of 184 ± 13 MPa at 1100 °C. With an increased heating rate to 10 °C/min, the strength loss at 750 °C persisted, but maximum CS was halved when firing at 900 °C. At 1100 °C, a significant reduction of CS was observed, but all samples maintained their integrity. Except for 1100 °C at 10 °C/min, all sintered-AAMs presented residual CS above 40 MPa. These results demonstrate that CaO-FeOx-Al2O3-SiO2-rich AAMs present interesting thermal behavior and can be potentially used to produce glass-ceramics or refractory materials from secondary resources.

Lightweight Cement-Based Composites Incorporating Hollow Glass Microspheres: Fresh and Hardened State Properties

This research aims to develop a lightweight cementitious composite with satisfied mechanical and good thermal insulating properties. Two different types of hollow glass microspheres were used as lightweight aggregates and were substituted with fine aggregate by 10, 20 and 40% by volume. The rheological, physical, mechanical and microstructural properties of the resulting HGM-incorporated composites are investigated. The results showed that physical and mechanical properties of individual HGM particles plays a dominant role on the properties of lightweight cement mortars. HGM addition provided reductions up to 20% in the density and 45% in the thermal conductivity values of mortars compared to the reference. The optimum HGM ratio is suggested as 20%, which provides benefits such as reduced density and improved thermal insulation capability without causing significant reduction in compressive strength. It was concluded that HGMs can be used in the lightweight cementitious mortar production which have great potential in building applications to reduce the heating energy consumption.

An Innovative Method for Sustainable Utilization of Blast-Furnace Slag in the Cleaner Production of One-Part Hybrid Cement Mortar

Hybrid cement (HC) can be defined as alkali activated-blended-Portland cement (PC). It is prepared by the addition of an alkaline solution to high-volume aluminosilicate-blended-PC. Although this cement exhibits higher mechanical performance compared to conventional blended one (aluminosilicate–PC blend), it represents lower commercial viability because of the corrosive nature of alkaline solution. Therefore, this study focuses on the preparing one-part HC using dry activator–based BFS (DAS). DAS was prepared by mixing sodium hydroxide (NaOH) with BFS at low water to BFS ratio, followed by drying and grinding to yield DAS-powder. Different contents of DAS (equivalent to 70 wt.% BFS and 1, 2, and 3 wt.% NaOH) were blended with 30 wt.% PC. A mixture containing 70 wt.% BFS and 30 wt.% PC was used as a reference sample. The mortar was adjusted at a sand–powder (BFS-PC and/or DAS-PC) weight ratio of 3:1. The microstructural analysis proved that DAS-powder is mainly composed of sodium calcium aluminosilicate–activated species and unreacted BFS. These species can interact again with water to form calcium aluminum silicate hydrate (C-A-S-H) and NaOH, suggesting that the DAS acts as a NaOH-carrier. One-part HC mortars having 1, 2, and 3 wt.% NaOH recorded 7th day compressive strength values of 82%, 44%, and 27%, respectively, higher than that of the control sample. At 180 days of curing, a significant reduction in compressive strength was observed within the HC mortar having 3 wt.% NaOH. This could be attributed to the increase of Ca (within C-S-H) replacement by Na, forming a Na-rich phase with lower binding capacity. The main hydration products within HC are C-S-H, C-A-S-H, and chabazite as part of the zeolite family.

Strength and Biocompatibility of Heparin-Based Calcium Phosphate Cement Grafted with Ferulic Acid.

The biomimetic synthesis of carbonated apatites by biomolecule-based templates is a promising way for broadening apatite applications in bone tissue regeneration. In this work, heparin was used as an organic template to prepare uniform carbonate-based apatite nanorods (CHA) and graft ferulic acid (F-CHA) for enhanced bone mineralization. Next, by combining calcium phosphate cement (CPC) with different F-CHA/CPC ratios, a new type of injectable bone cement combined with F-CHA bioactive apatite was developed (CPC + F-CHA). The physicochemical properties, biocompatibility, and mineralization potential of the CPC + F-CHA composites were determined in vitro. The experimental results confirmed the preparation of highly biocompatible CHA and the compatibility of F-CHA with CPC. Although CPC + F-CHA composites with F-CHA (2.5 wt%, 5 wt%, and 10 wt%) showed a significant reduction in compressive strength (CS), compositing CPC with 10 wt% F-CHA yielded a CS suitable for orthopedic repair (CS still larger than 30 MPa). Spectroscopic and phase analyses revealed that the phase of the hydrothermally synthesized CHA product was not modified by the heparin template. Injection and disintegration tests indicated that the CPC + F-CHA composites have good biocompatibility even at 10 wt% F-CHA. D1 osteoprogenitor cells were cultured with the composites for 7 days in vitro, and the CPC + 10%F-CHA group demonstrated significantly promoted cell mineralization compared with other groups. Given these results, the use of over 10% F-CHA in CPC composites should be avoided if the latter is to be applied to load-bearing areas. A stress-shielding device may also be recommended to stabilize these areas. These newly developed biocompatible CPC + F-CHA have great potential as osteoconductive bone fillers for bone tissue engineering.

Water transport and resistance improvement for the cementitious composites with eco-friendly powder from various concrete wastes

The water transport properties of cementitious composites are the key parameters to evaluate the durability performance. This work gives an investigation on the impact of RP type, substitution rate and particle size on the water transport in cementitious composites, and the feasible methods of improving the water transport resistance are further investigated. Utilizing recycled paste powder (RPP), recycled mortar powder (RMP) and recycled concrete powder (RCP) produced from various concrete waste is detrimental to the hydration reaction and pore structure of cementitious composites, and the total porosity of paste incorporating 30% various RPs is 35.4–36.0% higher than that of plain paste. Utilizing RP decreases the compressive strength of cementitious composites, and a significant reduction in compressive strength occurs when RP substitution rate is 50%. The water transport in cementitious composites is increased by incorporating RP, and the RMP-prepared and RCP-prepared mortar have lower water absorption than the RPP-prepared mortar; for example, the absorption coefficient of the mortar containing 30% RPP, RMP and RCP is 72.7%, 44.9% and 48.7% greater than that of plain mortar without RP. Besides, the water transport in the mortar incorporating fine particle RP is lower than that in the mortar containing coarse particle RP. Co-mixing RP and mineral admixtures decreases the water transport in cementitious composites, and the mortar incorporating 20% RP and 10% metakaolin (or 10% silica fume) has lower water absorption and slightly higher compressive strength than plain mortar without RP.

Strength Characteristic of Recycled Aggregate with Silica Fume as Admixture

In this study, conventional concrete is developed using recycled aggregates with micro silica (silica fume) as admixture. The concrete mix is designed for target strength of 25 MPa. Coarse aggregate were partially with recycled aggregate at 15 %, 30 % and 45 %. The relative parameters influencing the strength of concrete were studied in terms of recycled aggregate and silica content respectively. Test results reveled concrete produced with 45% of recycled aggregate tend to reduce the strength by 12% whereas addition of silica fume (10%) enhances the strength comparable to control mix (M25). Addition of microsilica functions as microfilling action in unreacted core of concrete which enhances the physical and mechanical properties of concrete. The significant reduction in compressive strength is noticed, when the recycled aggregate is increased beyond 30%.

Class C fly ash-based alkali activated cement as a potential alternative cement for CO2 storage applications

Long-term storage of carbon dioxide (CO2) inside depleted reservoirs can help reduce the impact of greenhouse gas emissions. Portland cement has been shown to degrade significantly during long-term contact with CO2. This research aims to provide a new environmentally friendly, Class C fly ash-based cement as a potential alternative to Portland cement for CO2 storage wells. This was achieved by comparing the mechanical degradation of Portland cement and Class C fly ash-based alkali-activated cement in a CO2 environment. A specially designed setup was constructed to create an in situ high pressure and high-temperature CO2 environment. Seventy-two cores of Portland cement and Class C fly ash-based cement were prepared for this study. The results show that CO2 reacted with the water in the vessel and formed carbonic acid, which reduced the water pH to 6.8. Millimeter-sized crystals of calcium carbonate (CaCO3) were observed on the surface of the Portland cement cores after the CO2 exposure. The surface of the fly ash-based alkali-activated cement cores was not substantively changed after the exposure. No significant change in density was observed for both types of cement during the 14 days of CO2 exposure. Portland cement showed a significant reduction in compressive strength, and this reduction developed as the exposure time increased. Interestingly, Class C fly ash-based cement showed no reduction in compressive strength, and only a small amount of reduction was observed after 14 days of exposure. This research compared the mechanical degradation of Portland cement and Class C fly ash-based alkali-activated cement in a high-pressure and high-temperature CO2 environment.

Chloride Ingress in Cement Mortars Exposed to Acidithiobacillus thiooxidans Bacteria

Concrete structures placed in aggressive aqueous environments are vulnerable to degradation. Majority of studies have linked structural failures to the ingress of deleterious ions into the cement matrix. Some microbial activities may accelerate the penetration of harmful materials into the cement matrix and hence cause pronounced deterioration. This work reports a laboratory‐simulated study carried out to determine the extent of chloride ingress in cement mortars exposed to Acidithiobacillus thiooxidans. Test prisms were cast from Portland pozzolana cement (PPC) and ordinary Portland cement (OPC) with water‐to‐cement ratio maintained at 0.5. Acidithiobacillus thiooxidans bacterial solution of concentration 1.0 × 107 cell/mL was used to prepare microbial mortar prisms, whereas distilled water was used to prepare the control mortar prisms. The test prisms were subjected to porosity and accelerated chloride ingress after 28th day of curing. Compressive strength was determined after the 2nd, 7th, 28th, and 56th days of curing. Apparent diffusion coefficients (Dapp) were estimated from the solutions to Fick’s second law of diffusion. After the 56th day of curing, the microbial‐treated mortars exhibited a significant reduction in compressive strength. The resultant percentage decrease in compressive strength was 30.74% and 19.88% for OPC and PPC, respectively. Further, microbial‐treated mortars demonstrated both high porosity and chloride ingress as compared to the control test mortars. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) analyses showed the formation of new deleterious products in the microbial‐exposed mortars.

High Volume Slag and Slag-Fly Ash Blended Cement Pastes Containing Nano Silica

This paper presents the effect of nanosilica (NS) on compressive strength and microstructure of cement paste containing high volume slag and high volume slag-fly ash blend as partial replacement of ordinary Portland cement (OPC). Results show that high volume slag (HVS) cement paste containing 60% slag exhibited about 4% higher compressive strength than control cement paste, while the HVS cement paste containing 70% slag maintained the similar compressive strength to control cement paste. However, about 9% and 37% reduction in compressive strength in HVS cement pastes is observed due to use of 80% and 90% slag, respectively. The high volume slag-fly ash (HVSFA) cement pastes containing total slag and fly ash content of 60% exhibited about 5%-16% higher compressive strength than control cement paste. However, significant reduction in compressive strength is observed in higher slag-fly ash blends with increasing in fly ash contents. Results also show that the addition of 1-4% NS improves the compressive strength of HVS cement paste containing 70% slag by about 9-24%. However, at higher slag contents of 80% and 90% this improvement is even higher e.g. 11-29% and 17-41%, respectively. The NS addition also improves the compressive strength by about 1-59% and 5-21% in high volume slag-fly ash cement pastes containing 21% fly ash+49%slag and 24% fly ash+56%slag, respectively. The thermogravimetric analysis (TGA) results confirm the reduction of calcium hydroxide (CH) in HVS/HVSFA pastes containing NS indicating the formation of additional calcium silicate hydrate (CSH) gels in the system. By combining slag, fly ash and NS in high volumes e.g. 70-80%, the carbon footprint of cement paste is reduced by 66-76% while maintains the similar compressive strength of control cement paste. Keywords: high volume slag, nanosilica, compressive strength, TGA, high volume slag-fly ash blend, CO2 emission.