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In our earlier study, the impact resistance of slabs made up of concrete containing hybrid fibers (i.e., steel and synthetic fibers in various proportions) was evaluated through an experimental program. The test specimens, measuring 600 × 600 × 90 mm, were cast with varying amounts of fibers, while some were kept as control samples without any fibers. The high-velocity impact tests were conducted using a gas-gun system, where hemispherical steel projectiles were fired at the slabs. The craters’ sizes and penetration depths were measured. The hybrid fibers in the concrete reduced spalling and scabbing damage and reduced the size of craters. In the current study, the impact response of the hybrid fiber-reinforced concrete (HFRC) slabs was investigated numerically. LS-DYNA software was employed for this investigation, and crack sizes, areas of spalling and scabbing damages, and penetration depths were estimated. The numerical simulations provided an efficient and practical tool for analyzing the HFRC slabs’ response against impact load. The use of hybrid fibers decreased front surface damage and prevented concrete particles from flying out of the back face. The inclusion of fibers in concrete increased the perforation energy by 49%–203%. The numerical predictions of penetration depth were reasonably close, with absolute errors varying from 3.6%− 32.6%, and the error in the prediction of maximum rebar strain varied from 2.5% to 12.7%. The presented model thus has the capability to predict the local damages of various types of RC and HFRC slabs with acceptable accuracy.

Composite walls consist of two reinforced concrete (RC) walls with or without a filling between them. The use of RC composite walls instead of thick monolithic concrete walls can save material costs significantly. However, it is still unknown if a composite wall system with some granular filling can provide impact resistance comparable to a monolithic RC wall. The objective of this experimental study was to investigate the effect of granular fillings between the two RC walls in improving the impact potential of composite walls and compare the behavior of such walls with that of an equivalent monolithic RC wall. For this purpose, the specimens were prepared to simulate monolithic and composite RC walls. These specimens were tested with a gas gun under single and multiple/repetitive impact loading using hemispherical nose projectiles. The composite walls’ response was then studied and compared with the response of monolithic and no-filling composite walls. Test results and the analysis of the results demonstrate that the idea of using a composite wall system is very promising as the impact response of a composite wall system is much improved than a monolithic wall of the same total thickness and reinforcement. The ballistic limit of the composite wall was also found. In order to predict the ejected mass from a composite wall system, a new analytical model was proposed. There was reasonable agreement between the test results and the prediction.

This paper experimentally investigates the dowel action contribution of longitudinal reinforcement, a hybrid of steel and GFRP bars (usually adopted for avoiding corrosion of steel bars), in concrete deep beams for different reinforcement schemes. The self-consolidating concrete without and with steel fibers (0.9 % and 1.2 % by volume) was used. Sixteen simply supported deep beams of 140 × 300 (depth) × 1500 mm were tested under the two-point loads. A model is developed to predict the shear capacity of deep beams without web reinforcement, taking into consideration the dowel action contribution of longitudinal reinforcement, which is a hybrid of steel and GFRP rebars. The results showed a significant dowel action contribution of steel as well as GFRP rebars to beam shear strength. However, the use of a hybrid system of steel and GFRP bars caused a reduction in the dowel action of steel bars due to their combined action.

Glass fiber-reinforced polymer (GFRP) bars are emerging as a potential replacement for steel rebars due to their vulnerability to corrosion. However, the shear behavior of GFRP bars is not well established, especially in functionally graded self-compacting concrete (SCC) deep beams reinforced with hybrid rebars (GFRP and steel). This article experimentally explores the behavior of functionally graded high-strength SCC deep beams having a hybrid of steel and GFRP bars as tension reinforcement. A total of fourteen deep beams were prepared with varying reinforcement ratios and steel fiber volume fractions. There were three groups of deep beams: (i) plain SCC (i.e., no fibers) beams, (ii) fiber-reinforced SCC (FRSCC) beams having 0.6 % and 1.2 % steel fibers, and (iii) functionally graded deep beams. The functional grading was achieved by casting beams in two layers, with the first layer of lower two-thirds depth having steel fibers and the second layer without fibers. The beams were shear deficient and tested in flexure. The shear resistance of functionally graded deep beams was compared with beams having fibers in full depth and without fibers. The test results reveal the significance of the hybrid system of rebars, which is found to effectively improve the structural capacity of concrete beams and increase the load required to initiate cracking. In addition, the mixing of fibers in concrete enhanced the deep beam shear capacity by 15–23 % for 0.6 % fibers and 37–39 % for 1.2 % fibers. The increase in the shear resistance of concrete deep beams was not influenced by the use of hybrid rebars compared to using GFRP bars only. A model is developed for assessing the shear resistance of functionally graded fiber-reinforced concrete deep beams by incorporating the dowel action of hybrid longitudinal reinforcing bars. The study indicates that the dowel action provided by GFRP bars is comparable to the steel bars of the same area.

In the Middle East, wall-like reinforced concrete (RC) columns are a common choice in multistory buildings. Sometimes, these columns need axial retrofitting for increased load capacity. In practice, unstrengthened columns bear their load, and if retrofitting is necessary, the load is released before the upgrade—unlike in past research studies that overlooked this real-world scenario. This study aimed to investigate the response of preloaded wall-like RC columns after being retrofitted using different configurations. In the experimental campaign, two half-scale columns were cast and axially loaded to 80% of their capacity, and the load was then totally released. After that, these specimens were strengthened with two different schemes, and hence, they were concentrically loaded until failure. In both schemes, the section shape was not modified. The first scheme comprised wrapping carbon FRP (fiber-reinforced polymer) sheets together with near-surface mounted (NSM) steel rebars. However, the second technique was composed of wrapping glass FRP (GFRP) sheets together with NSM steel rebars and bolted steel plates. The second scheme was found to be superior to the first one due to the extra confinement provided by the bolted steel plates. This scheme improved the peak load, stiffness, and dissipated energy by 115%, 75%, and 524%, respectively. Other than the testing campaign, nonlinear numerical modeling was undertaken to examine the behavior of tested specimens. The models were utilized to conduct a parametric study, exploring the influence of the percentage of preloading and the amount of load release on the response of columns strengthened with the second scheme.

The concept of microbially induced calcite precipitation (MICP) is in vogue for quite some time; but a multitude of factors that would lead to optimal bacterial activity enabling real time application of the technique in various intended processes are yet to be standardized. This study is an attempt to elucidate some of these factors. The study was conducted in sand columns simulating standard cement mortar conditions of high pH at room temperature. Sporosarcina pasteurii ATCC6453 cultures in broths at variable cell counts of 1 × 103, 105, 107, and 109 ml−1 with 0.2M concentrations of urea and calcium chloride were poured onto sand columns in plastic sheet molds. After variable incubation period of 24, 48, 72, and 96 h, urease activity of the bacterium was assayed calorimetrically. Physical verification of calcite deposition was done with scanning electron microscopy (SEM) and X-ray diffraction (XRD) after 28 days of treatment. Urease activity escalated significantly with increasing cell count and incubation period. SEM and XRD examinations revealed remarkable deposition of calcite in the columns under treatment.

Increasing demand for concrete construction and the consequent increase in the production of conventional Portland cement is thwarting efforts towards sustainable construction practices. This is seen in the carbon dioxide footprint caused by cement manufacturing as well as natural resources consumption. Therefore, the so-called geopolymer or alkali-activated composites using byproduct or natural materials are seen as a potential substitute for cement-based binders. Similarly, recycled rubber recovered from shredded tires has been used in concrete mixes, which in addition to the environmental benefit, offers desirable properties, e.g., improved deformability and energy dissipation capacity. Therefore, this paper investigates the influence of introducing recycled rubber in metakaolin-based geopolymer mixes on the workability, compressive behavior (stress–strain components and failure mode), flexural strength, unit weight, air content, and water absorption percentage. Seven mixes were employed for this purpose with two main variables comprising rubber size (fine, coarse, or combination of both) and replacement percentage (0%, 20%, and 40%). Recycled rubber was observed to reduce the mix workability by 4%–52.5% and 40%–62.5% when fine or coarse rubber particles were added to concrete mixes, respectively. Average compressive strength of 14.3–37.7 MPa was achieved when fine and/or coarse rubber particles replaced 20% or 40% of the conventional fine and/or coarse aggregates. Furthermore, rubberized geopolymer concrete showed more deformability than plain mixes coupled with lightweight characteristics, which are desirable in many construction applications. This indicates the suitability of the rubberized geopolymer concrete for developing low to moderate-strength concrete for non-structural and structural applications.

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings.

Damage induced by fire is considered a serious threat to reinforced concrete structures during their useful lifetime. While concrete is a non-flammable material, its exposure to fire affects its stress-strain characteristics and durability. Given that a full replacement and/or demolition option is economically inefficient for fire-damaged structures, a better alternative for lengthening their service life involves repair or strengthening the damaged members. The current testing program primarily investigated the influence of strengthening by glass fiber reinforced polymer (GFRP) sheets on the behavior of heat-damaged plain and fiber-reinforced normal and high strength concretes. Strengthening was considered for concrete cylinders after being exposed to 400 °C and 600 °C temperature and left to cool by air cooling or water quenching. Fiber-reinforced concrete (FRC) mixes were cast with steel, polypropylene, or a hybrid of steel and polypropylene fibers. For plain and various fiber-reinforced normal strength concretes exposed to 400 °C and cooled by ambient air cooling or water quenching, the compressive strength of GFRP confined concrete increased by 39% to 48% and 42% to 56%, respectively (in comparison to the unheated specimens). However, this enhancement was observed to be higher for concretes heated at 600 °C.

Steel buildings are generally susceptible to the risk of progressive collapse in case one or a few load-carrying members are lost in an extreme event such as blast, impact, or fire. Thus, to avoid the catastrophic collapse of steel structures, it is imperative to investigate and learn from the performance of existing steel buildings for progressive collapse potential. The Ohio Union building, a multi-story steel-framed building that existed on the campus of Ohio State University, was tested earlier before its demolition by one of the co-authors for progressive collapse assessment under the successive removal of four columns located at the first-story level. The aim of this study is to conduct NLD (nonlinear dynamic) analysis for the building considering buckling of columns to numerically assess its potential for progressive collapse and then compare it with test observations. The calibrated finite element (FE) model was then extended to incorporate more hypothetical sequential and simultaneous column-loss scenarios. As one of the most widely accepted documents used among practicing engineers for numerical assessment of progressive collapse potential of buildings, the 2003 GSA (General Services Administration) guidelines were also applied. The simplified LS (linear static) analysis approach of the GSA guidelines was used for assessing the progressive collapse risk of the building, and the results were then compared with both test observations and NLD analysis. New dynamic increase factors (DIFs) are recommended for both force- and deformation-controlled actions to be used with the LS analysis.

Reinforced concrete (RC) wall-like columns are commonly employed in structures in Saudi Arabia. These columns are preferred by architects owing to their minimum projection in the usable space. However, they often need strengthening due to several reasons, such as the addition of more stories and increasing the live load as a result of changing the usage of the building. This research aimed to obtain the best scheme for the axial strengthening of RC wall-like columns. The challenge in this research is to develop strengthening schemes for RC wall-like columns, which are favored by architects. Accordingly, these schemes were designed so that the dimensions of the column cross-section are not increased. In this regard, six wall-like columns were experimentally examined in the event of axial compression with zero eccentricity. Two specimens were not retrofitted to be used as control columns, whereas four specimens were retrofitted with four schemes. The first scheme incorporated traditional glass fiber-reinforced polymer (GFRP) wrapping, while the second one utilized GFRP wrapping combined with steel plates. The last two schemes involved the addition of near-surface mounted (NSM) steel bars combined with GFRP wrapping and steel plates. The strengthened specimens were compared with regard to axial stiffness, maximum load, and dissipated energy. Besides column testing, two analytical approaches were suggested for computing the axial capacity of tested columns. Moreover, finite element (FE) analysis was performed for evaluating the axial load versus displacement response of tested columns. As an outcome of the study, the best strengthening scheme was proposed to be used by practicing engineers for axial upgrading of wall-like columns.

The use of fiber reinforced polymer (FRP) rebars is nowadays becoming popular in reinforced concrete (RC) construction due to their excellent inherent properties such as corrosion resistance, lightweight, and high strength to weight ratio. The steel rebars, being susceptible to corrosion, are being replaced by FRP rebars. The higher strength of FRP rebars, as compared to steel, requires larger lap lengths when embedded in concrete. Although laps in steel rebars can be replaced by mechanical couplers, this is not feasible for FRP rebars. Thus, the present study investigates the use of couplers for Glass FRP (GFRP) rebars. Three types of couplers were tried: (i) steel pipe coupler, (ii) CFRP pipe coupler, and (iii) CFRP sheet coupler. These couplers were tested in direct tension for assessing their feasibility and establishing the design requirements. Although the steel pipe coupler demonstrated excellent performance, the use of CFRP pipe and CFRP sheet couplers were not successful. However, the performance of CFRP sheet couplers can be improved by increasing the length of sheet, and/or number of wraps.

Geopolymer is emerging as a potential alternative material to the ordinary Portland cement (OPC) owing to its energy efficiency and environmental protection. However, the effect of the mix design parameters on the behavior of geopolymer concrete (GPC) produced using local metakaolin (MK) is not well established. This paper presents findings from a comprehensive experimental program to study the effect of various mix design parameters on the properties of fresh and hardened MK-based GPC. Seventeen mixes were cast in four groups to investigate the effect of four parameters, including sodium silicate to sodium hydroxide ratio, alkaline solids to MK ratio, aggregate content, and water to solids ratio on the properties of GPC. The investigated properties included workability, density (wet and dry), development of compressive strength with age, splitting tensile strength, ultrasonic pulse velocity, water absorption, and horizontal abrasion resistance. Besides, two reference OPC concrete mixes, equivalent to two MK-based geopolymer mixes, were tested for the sake of comparison. The test results were helpful in developing a better understanding of the behavior of MK-based GPC. Some useful models are proposed for predicting workability, splitting tensile strength, water absorption, and weight loss in abrasion for MK-based GPC. The test results were supplemented and confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analysis performed on some selected GPC mixes.

In RC (reinforced concrete) frame structures, wall-like columns are laid within the space occupied by masonry walls to maximize usable space and thus minimize the column projections into the usable area. These columns often require strengthening owing to various reasons, including increasing the number of stories, changes in building usage, and others. The use of a hybrid system comprising NSM (near-surface mounted) steel rebars combined with CFRP (carbon-fiber reinforced polymer) laminates may be considered a sound technique for strengthening such wall-like building columns. The prime aim of this study is to devise an efficient scheme using a hybrid NSM/CFRP system to strengthen existing RC wall-like columns. Six half-scale RC wall-like columns were prepared and tested under monotonic concentric axial compression. Two columns were unstrengthened to serve as control specimens (CW1 and CW2), and four specimens were strengthened using four different schemes (SW1, SW2, SW3, and SW4). As favored by architects, all strengthening schemes were designed so that the dimensions of the column cross-section were not increased. The effects of strengthening schemes on the enhancement of axial capacity, energy dissipated, and stiffness were evaluated to find the most efficient scheme. Among the four studied schemes, using vertical continuous NSM rebars in combination with the wrapping of the three CFRP layers onto the exterior column surface (in specimen SW2) was the most efficient as it enhanced the ultimate load capacity by 80%. Three-dimensional FE (finite element) analysis was also conducted to predict the response of test specimens. The test results matched well with the FE outputs, which justified the accuracy of the used constitutive models for concrete, steel rebars, and CFRP sheets.

Ordinary Portland cement (OPC) is commonly adopted as an effective binder in the production of concrete and cementitious mortars. The metakaolin (MK) based geopolymer (GP) binder offers a sustainable alternative to the OPC due to its essential environmental and technical benefits in reducing the carbon footprint. In the present study, two conventional and six GP repair mortars were used. Three GP mortars were plain (without fibers), and the remaining three were produced by mixing Polyvinyl-alcohol (PVA) fibers. The GP mixes were produced by varying sand content, alkaline solids to MK, and sodium silicate to NaOH ratios, resulting in different molar ratios. The test specimens were prepared by overlaying a 5 mm thick layer of repair mortar on a concrete substrate for conducting pull-off strength tests. This research was undertaken to investigate the effect of exposure to elevated temperatures on the performance of bond strength of GP mortar used as a repair material. The test specimens were subjected to ambient temperature and elevated temperatures of 200 and 400 °C for a duration of 3 h before conducting pull-off tests. The test results revealed that the selected GP mixes could be a promising alternative repair material for structures due to their good bond strength performance. The addition of fibers in stable mixes of GP mortars enhanced the bond strength at ambient as well as when exposed to 200 °C, through crack control mechanism.

Concrete is classified as a multi-composite material comprising three phases: coarse aggregate, mortar, and interfacial transition zone (ITZ). Fine and coarse aggregates occupy approximately 70–85% by volume, of which coarse aggregate typically constitutes more than two-thirds of the total quantity of aggregate by volume. The current study investigates the concrete performance produced using various recycled construction and by-product industrial waste coarse aggregates. Six types of coarse aggregates: manufactured limestone, quartzite, natural scoria, by-product industrial waste aggregate, and two sources of recycled concrete aggregates with densities ranging from 860 to 2300 kg/m3 and with different strength properties were studied. To determine the coarse aggregate contribution to the overall concrete performance, lean and rich concrete mixtures (Mix 1 and Mix 2) were used. Mix 1 (lean mixture) consisted of a ratio of water to cement (w/c) of 0.5 and cement content of 300 kg/m3, whereas a higher quantity of cement of 500 kg/m3 and a lower w/c ratio of 0.3 were used for Mix 2 (rich mixture). The results showed that while the compressive strength for different aggregate types in Mix 1 was comparable, the contribution of aggregate to concrete performance was very significant for Mix 2. Heavyweight aggregate produced the highest strength, while the lightweight and recycled aggregates resulted in lower mechanical properties compared to normal weight aggregates. The modulus of elasticity was also substantially affected by the coarse aggregate characteristics and even for Mix 1. The ACI 363R-92 and CSA A23.3-04 appeared to have the best model for predicting the modulus of elasticity, followed by the ACI-318-19 (density-based formula) and AS-3600-09. The density of coarse aggregate, and hence concrete, greatly influenced the mechanical properties of concrete. The water absorption percentage for the concrete produced from various types of aggregates was found to be higher for the aggregates of higher absorption capacity.

Experimental and numerical investigations on the retrofitting of half-scale wall-like reinforced concrete (RC) columns were conducted. The axial compressive behavior of the control un-strengthened wall-like RC column (having a section aspect ratio of four) was compared with the strengthened columns. The columns were strengthened by employing external confinement through fiber-reinforced polymer (FRP) wraps and/or steel/FRP strips with/without modification of the column cross-section. The characteristics of axial load versus displacement and strain curves were discussed. The experimental results were also compared with the numerical models, which were first validated against the previous studies. A reasonably close agreement was achieved between the numerical and the test results with an error in prediction of less than 10% for the peak load. With the different schemes used for confinement, the enhancement in the load capacity of strengthened columns was in the range of 30–42% of the control column. In addition, significant ductility improvements were seen in schemes that employed the FRP wraps after shape modification.

A simulation-based probabilistic method is proposed for assessing the reliability of steel-lined and prestressed fiber-reinforced concrete (PFRC) slabs against the impact loads. The impact testing of several prestressed and non-prestressed FRC slabs of 800 × 800 × 100 mm in size was carried out. The experimental program involved projectile impact testing of prestressed and non-prestressed FRC slabs using a gas gun. Three parameters were varied for testing of slabs under the projectile impact, viz., a quantity of steel fibers in the concrete, steel lining on the backside of the slab, and the prestressing level. The probability-based reliability analysis of all the tested specimens was then performed to highlight the influence of steel lining, steel fibers, and prestress in enhancing the safety of RC (reinforced concrete) slabs against projectile impacts. Projectile impact velocity exceeding the slab’s ballistic limit was assumed to lead to the failure of the PFRC slab, i.e., the perforation failure of the slab. Study results indicate that when no steel fiber was present, slab reliability was low. Adding fibers to slabs increases slabs’ reliability significantly. Specimens with the highest steel fiber content (1.2%) showed the greatest increase in reliability. The steel lining on the back face makes the slab’s reliability almost doubled in comparison with those without lining. Additionally, steel lining makes the PFRC slabs as reliable as desired. It was further noticed that the prestressing helps in enhancing the slab safety against projectile impacts. Even a minimal amount of prestressing makes a noticeable improvement in the reliability of PFRC slabs.

The formulas available in the literature for predicting the projectile impact response of reinforced concrete (RC) targets are generally developed based on the results of impact tests. Recently, however, in order to avoid performing involved and challenging projectile impact tests, the impact response of RC targets was predicted using the quasi-static punching response of RC slabs. In this paper, the concept is extended to concrete slabs strengthened with textile-reinforced mortar (TRM) or carbon fiber-reinforced polymer (CFRP) sheets externally bonded to the concrete surface. In 16 groups, 96 slabs of 600 × 600 × 90 mm size were cast and tested under quasi-static and impact loads. The slabs were reinforced with two types of reinforcement: ϕ8@100 mm and ϕ4@25 mm. The singly and doubly reinforced concrete slabs with rebar spacing of 100 mm were strengthened using externally bonded CFRP and TRM on the back side of the slab specimens. Two mixes of concrete, representing normal and high-strength concretes, were used. The results of the present study reveal that the CFRP and TRM strengthening of RC slabs enhanced the energy absorption in punching by 57–130% and 20–59%, respectively. The use of WWM in singly and doubly reinforced slabs also resulted in a 30–42% and 41–63% increase in energy absorption in punching, respectively. An earlier proposed model was modified to incorporate the influence of strengthening (CFRP and TRM) in the estimation of the projectile perforation energy of the strengthened RC slabs with the help of energy absorbed in their quasi-static punching. This perforation energy was then employed for predicting the ballistic limit of CFRP- and TRM-strengthened slabs. The predictions show good agreement with the experimentally observed ballistic limits.

Abstract This paper aims to investigate the behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams containing large rectangular web openings in the flexure zone. Studied parameters were type of loading, opening size and strengthening scheme. Seven RC beams categorized into two different groups were tested. In the first group, two unstrengthened beams (one solid without opening and one with large rectangular web opening in the pure flexure zone) were tested under four-point bending. In the second group, five beams were tested under center-point loading. They comprised of one reference solid beam and four beams with large rectangular web opening in the maximum-moment region. Out of the four beams with openings, two specimens were unstrengthened and the other two were strengthened with two different FRP schemes. A numerical study was also conducted and the results of analysis were validated with experiments. The calibrated analysis was then used for some useful parametric studies in which the effect of different parameters was investigated.

Sporosarcina pasteurii, a common soil bacterium has been tested for microbial treatment of cement mortar. The present study also seeks to investigate the effects of growth medium, bacterial concentration and different buffers concerning the preparation of bacterial suspensions on the compressive strength of cement mortar. Two growth media, six different suspensions and two bacterial concentrations were used in the study. The influence of growth medium on calcification efficiency of S. pasteurii was insignificant. Significant improvement in the compressive as well as the tensile strength of cement mortar was observed. Microbial mineral precipitation visualized by Scanning Electron Microscopy (SEM) shows fibrous material that increased the strength of cement mortar. Formation of thin strands of fillers observed through SEM micrographs improves the pore structure, impermeability and thus the compressive as well as the tensile strengths of the cement mortar. The type of substrate and its molarity have a significant influence on the strength of cement mortar.

Abstract The paper presents experiments involving punching of RC slabs strengthened using externally bonded carbon fiber reinforced polymer (CFRP) sheet and textile reinforced mortar (TRM). Twelve RC slab specimens of two concrete grades (39.9 and 63.2 MPa) and employing two strengthening schemes (CFRP and TRM) were tested. Specimens were supported on two opposite edges. Experimental load-displacement variations show two peak loads in strengthened slabs and one peak followed by a plateau in control. Second peak or the plateau corresponds to the combined action of aggregate interlock and the dowel action of back face rebars and strengthening layers. The dowel action of back face rebars and strengthening layers had no role in ultimate punching load (i.e. first peak). Strengthened slabs showed 9-18% increase in ultimate punching load (i.e. first peak) whereas there was significant increase in the second peak load (190-276% for CFRP; 55-136% for TRM) and energy absorption (~66% for CFRP and 22-56% for TRM). An analytical model was also developed for predicting the punching shear strength (first and second peaks) of strengthened slabs showing good comparison with experiments.