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Structures exposed to high temperatures must have enhanced thermal stability and mechanical properties. It is essential to utilise sustainable materials in the endeavour to achieve this objective. This study investigates the combined effects of natural rubber latex (NRL) and hybrid fibres in high-volume fly ash (HVFA) concrete. It introduces a novel approach of utilising NRL as a partial cement replacement at varying percentages of 2.5%, 5%, 7.5%, and 10%. Replacing cement with 2.5% NRL resulted in optimal performance. Higher percentages of NRL enhanced the concrete’s workability, with 10% NRL producing a maximum slump of 54 mm. Adding 2.5% and 5% NRL significantly reduced water absorption by 12–18% compared to the control sample. Compressive strength decreased with higher NRL contents. The smallest reduction of 8% occurred with 2.5% replacement, and the highest loss of 55% was at 10% replacement. In contrast, tensile and flexural strengths improved by 14% and 31%, respectively, after 28 days of curing. The concrete with 2.5% NRL retained more strength at elevated temperatures, with a loss of strength of 20% at 600 °C compared to 25% for the control. The microstructural analysis revealed that the optimal NRL percentage resulted in a denser matrix, supporting the mechanical results. Generally, incorporating 2.5% NRL with hybrid fibres in HVFA concrete enhances durability and thermal resistance while maintaining satisfactory strength, offering a sustainable approach for high-performance applications.

Although the use of 3D printing in civil engineering has grown in popularity, one of the primary challenges associated with it is the absence of steel bars inside the printed mortar. As a result, developing 3D printing mortar with ultra-high compressive, flexural, and tensile strengths is critical. In the present study, an ultra-high-performance mortar incorporating silica fume (SF) and graphene nanoplatelets (GNPs) was developed for 3D printing application. The concrete mixture added SF to the concrete mixture in the range between 0% and 20%, while GNPs were added as a partial replacement by cement weight from 0.5% to 2%. The flowability and the machinal properties of the proposed mortar, including compressive (CS), tensile (TS), and flexural strength (FS), were investigated and assessed. Microstructure analysis involving FESEM and EDX was also investigated and evaluated, while response surface methodology (RSM) was considered to predict and optimize the optimum value of GNPs and SF. Workability results show that the flowability is reduced when the amount of graphene increases. Based on the predicted and experimental results, ultra-high-strength mortar can be developed by including 1.5% of GNPs and 20% of SF, in which the CS jumped from 70.7 MPa to 133.3 MPa at the age of 28 days. The FS and TS were 20.66 MPa and 14.67 MPa compared to the control mix (9.75 MPa and 6.36 MPa), respectively. This favorable outcome was credited to the pozzolanic activity of SF and the effectiveness of GNPs in compacting the pores and bridging the cracks at the nanoscale level, which were verified by FE-SEM and EDX. In addition, the developed quadratic equations proved their accuracy in predicting and optimizing the mechanical properties with low error (less than 0.09) and high correlation (R2 > 0.97). It can be concluded that the current work is an important step forward in developing a 3D printing mortar. The lack of reinforcement in the printed mortar structure has been a considerable difficulty, and the SF and GNPs have increased the compressive, flexural, and tensile strengths of the mortar. Thus, these improvements will encourage the industry to utilize sustainable materials to produce more affordable housing.

Research on different prefabricated cementitious composites for constructing composite concrete columns is comparatively more limited than that of concrete filled steel tube columns. The main objective of this study was to observe the axial compressive behavior of concrete-filled prefabricated cementitious composite tube (CFPCCT) specimens. In the CFPCCT composite column, the spiral steel bar is arranged as a hoop reinforcement in the cementitious tube before its prefabrication. Following this, the concrete is poured into the prefabricated cementitious composite tube. The tube is able to provide lateral confinement and can carry the axial load, which is attributed to the strength of CFPCCT composite column. The effect of tube wall thickness on the behavior of CFPCCT is studied in this research. A total of eight short-scale CFPCCT composite columns, with three different tube wall thicknesses (25 mm, 30 mm and 35 mm), are tested under axial compressive load. The cementitious composite tube-confined specimens showed a 24.7% increment in load-carrying capacity compared to unconfined specimens. Increasing the wall-thickness had a positive impact on the strength and ductility properties of the composite column. However, poor failure behavior was observed for thicker tube wall. Therefore, concrete-filled cementitious composite tube columns can be considered as an alternative and effective way to construct prefabricated concrete columns.

This study investigated the structural behavior of a beam–slab member fabricated using a steel C-Purlins beam carrying a profile steel sheet slab covered by a dry board sheet filled with recycled aggregate concrete, called a CBPDS member. This concept was developed to reduce the cost and self-weight of the composite beam–slab system; it replaces the hot-rolled steel I-beam with a steel C-Purlins section, which is easier to fabricate and weighs less. For this purpose, six full-scale CBPDS specimens were tested under four-point static bending. This study investigated the effect of using double C-Purlins beams face-to-face as connected or separated sections and the effect of using concrete material that contains different recycled aggregates to replace raw aggregates. Test results confirmed that using double C-Purlins beams with a face-to-face configuration achieved better concrete confinement behavior than a separate configuration did; specifically, a higher bending capacity and ductility index by about +10.7% and +15.7%, respectively. Generally, the overall bending behavior of the tested specimens was not significantly affected when the infill concrete’s raw aggregates were replaced with 50% and 100% recycled aggregates; however, their bending capacities were reduced, at −8.0% and −11.6%, respectively, compared to the control specimen (0% recycled aggregates). Furthermore, a new theoretical model developed during this study to predict the nominal bending strength of the suggested CBPDS member showed acceptable mean value (0.970) and standard deviation (3.6%) compared with the corresponding test results.

Rapid growth in industrial development has raised the concern of proper disposal of the by-products generated in industries. Many of them may cause serious pollution to the air, land, and water if dumped in open landfills. Agricultural and municipal wastes also cause environmental issues if not managed properly. Besides, minimizing the carbon footprint has become a priority in every industry to slow down global warming and climate change effects. The use of supplementary cementitious materials (SCMs) obtained from agricultural, industrial, municipal, and natural sources can decrease a significant amount of fossil fuel burning by reducing cement production and contribute to proper waste management. Also, SCMs can enhance desirable material properties like flowability, strength, and durability. Such materials may play a big role to meet the need of modern time for resilient construction. The effective application of SCMs in cement-based materials requires a clear understanding of their physical and chemical characteristics. Researchers studied how the flowability, strength, and durability properties of structural mortar change with the replacement of cement with different SCMs. Various experiments were conducted to examine the behavior of structural mortar in extreme conditions (e.g., high temperature). Many scholars have attempted to improve its performance with various treatment techniques. This article is an attempt to bring all the major findings of the recent relevant studies together, identify research gaps in the current state of knowledge on the utilization of SCMs in structural mortar, and give several recommendations for further study. The available results from recent studies have been reviewed, analyzed, and summarized in this article. A collection of the updated experimental findings will encourage and ease the use of various by-products and wastes as SCMs in structural mortar for sustainable construction.

For decades, ferrocement has been used to repair, strengthen, and even build structural components because it is a long-lasting and reasonably priced material. However, onsite ferrocement jacketing is time-consuming and labour-intensive. Alternatively, prefabricated ferrocement jacket installation eliminates these shortcomings. Therefore, this study utilises wearable prefabricated ferrocement jackets to repair and strengthen axially loaded sub-standard low-strength concrete elements. In order to repair cracked specimens and strengthen existing intact specimens, two types of wearable prefabricated jackets are proposed, ‘L’ shape and ‘U’ shape. Besides a control specimen, two preloaded and two unloaded square concrete specimens were utilised to repair and strengthen using the Prefabricated Ferrocement Jacketing system. The test results and crack patterns show that all the jacketed specimens performed better than the control specimens in terms of load-bearing capacity, ultimate axial and lateral deflection, and ductility. In terms of load-bearing capacity, the unloaded strengthened specimens showed significant results consistently. Based on the results, the proposed solutions were found to be effective in solving the problem of typical square ferrocement jackets.

Schmidt rebound hammer test was employed in this study as a nondestructive test. This test method has been universally utilized due to its non-destructiveness for quick and easy assessment of material strength properties and quality of concrete of an existing structure. Industrial waste materials (air-dried alum sludge, treated alum sludge, limestone dust and quarry dust) were employed as replacement material for fine aggregates in this study. A normal strength concrete was designed to achieve 35 MPa at 28 days, with industrial waste materials replacing fine aggregate at different percentages (0%, 5%, 10% and 15%), and then cured for 7, 28 and 180 days. The compressive strength values and rebound numbers for all the mixes obtained were correlated, and a regression equation was established between compressive strength and Schmidt rebound number. The correlation result showed an excellent relationship between rebound number and compressive strength of concrete produced in this study at all curing ages, with correlation coefficients of R2 = 0.98, R2 = 0.99 and R2 = 0.98. The predicted equation showed a strong relationship with the experimental compressive strength. Therefore, it can be used for the prediction of compressive strength of concrete with industrial waste as a replacement for fine aggregate.

Compressive strength performance of concrete after exposure to the elevated temperature is important for evaluating and repairing concrete structures. This paper presents an experimental study to determine the residual compressive strength of concrete used in tunnel lining after exposed to tunnel fire. Two types of concrete tunnel lining segments are evaluated in this study. One of it was constructed using a patented fire-resistant concrete (MYC) containing high volume fly ash and nanosilica (HVFANS). Another concrete tunnel lining segment was constructed using concrete containing silica fume normally used in the current construction, coded as SPC concrete. The drilled core results show that, after exposure to tunnel fire temperature up to around 1045°C, the compressive strength of MYC has dropped to 66% of the design strength. In comparison, the SPC concrete showed a decrease in compressive strength to 62% of design strength. The experimental results confirmed that the SPC segments have shown slightly lower residual compressive strength compared to the MYC segments. However, the MYC tunnel segment shows high resistance to the spalling of cover concrete compared to the SPC tunnel segment. Therefore, it can be said that the residual strength alone is not sufficient to compare the damage of concrete exposed to tunnel fire; the spalling damage observation is similarly important as it is one of the important serviceability criteria for designing concrete structures.

The utilization of pozzolans in cementitious system (concrete and mortar) minimizes both cost and energy. It also enhances mechanical strength and durability of the system. The total contribution of pozzolans can be categorized into two: (i) physical or filler effect which is attributed by the fineness of the particles and (ii) chemical or pozzolanic effect which is attributed by the pozzolanic reaction. It is difficult to quantify the strength development of cementitious system caused by the filler and pozzolanic effect separately. Therefore, the individual contribution of pozzolans in cementitious system because of its physical and chemical effects need to be profoundly understood by the scientific community. This paper reviews available literatures to understand the effect of non-reactive fillers that attributed as the microfiller effect of pozzolans in cementitious systems. The previous studies utilized chemically inactive materials that attributed only the microfiller activity of pozzolans for a partial replacement of cement. It was reported that filler effect is equal or sometimes more significant than pozzolanic effect in concrete. A larger range of replacement percentages (like 5%, 10%, 15% or 10%, 20%, 30% etc.) was used in the previous studies. However, probabilities of the optimum compressive strength because of the filler effect may lie in between two larger range of replacement percentages. Therefore, an experimental work is also carried out using natural ground sand of size 7.6-μm at a lower range of cement replacement percentages (like 2.5%, 5%, 7.5% etc.) in mortar. Compressive strength of mortar at different ages and microstructure analysis of mortar at 28 days were performed in this study. Test results showed that the filler effect is more pronounced at a lower replacement percentages of cement (0-10%) while using smaller non-reactive fillers. The maximum strength due to filler effect of ground sand is acheieved at 7.5% replacement of cement. Scanning Electron Microscope (SEM) images also confirmed the effect of fillers on the microstructure development of mortar.

This study evaluated the effect of alum sludge as an alternative to fly ash in fabricating geopolymer paste and mortar. The blending of this industrial waste (alum sludge and fly ash) is not only for the benefit of sustainable construction and disposal of industrial waste but also for the reduction of CO2 emissions due to the increasing production of Portland cement from the cement production industry. A laboratory investigation was carried out on the workability and mechanical properties of geopolymer paste and mortar produced with alum sludge replacement in different proportions (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100). A combination of an alkaline solution of sodium silicate and sodium hydroxide of 14 molarity was employed as an activator for the manufacturing of both paste and mortar geopolymer specimens. It was observed from the findings that geopolymer paste and mortar was flowable and workable when alum sludge is replaced for fly ash at higher replacement content. The addition of alum sludge to the mix improved some properties such as density, strength, water absorption, and the elevated temperature behavior. It was observed that the addition of alum sludge was optimum at the 50% replacement level. The addition of alum sludge up to 50% significantly increased the compressive strength of mortar (up to 80% increase in 28 days strength). The compressive strength of the paste and mortar increased with an increase in curing age. Thus, alum sludge and fly ash can be employed together in the production of eco-friendly cementing material for environmental sustainability.