De-aluminated metakaolin-cement composite modified with commercial titania as a new green building material for gamma-ray shielding applications

Sustainable disposal of dealuminated metakaolin (DAK) is a crucial environmental issue for the alum production industry. In previous studies, DAK was utilized as eco-friendly cementitious materials, but only 10 wt% was used instead of cement as DAK's high percentage has a detri-mental effect on the mechanical properties, so the environmental problem of DAK has not yet been solved. In this study, commercial titanium oxide (TiO2) was incorporated in a cement matrix containing DAK that reached 50 wt% to benefit from TiO2's properties in enhancing the me-chanical performance of binding materials and producing cementitious blends used as blocking materials against harmful gamma radiation. Five pastes were prepared to reach the main target; ordinary Portland cement (OPC), OPC-10%DAK (D10), OPC-30%DAK (D30), OPC-50%DAK (D50) and OPC-45%DAK-5%TiO2 (D45-T5). By means of a mini-slump test, all fresh blends have very close flowability using the appreciated additions of polycarboxylate superplasticizer. The hardened composites were cured in tap water for up to 28-days. Compressive strength results at 28 days for OPC, D10, D30 and D50 were 80, 94.6, 60.8 and 57.6 MPa, respectively. An obvious turning point in strength value from 57.6 to 88 MPa after replacement of DAK by 5 wt% TiO2 (D45-T5). A gamma-ray shielding test was performed using two radioactive isotopes (Co-60 and Cs-137). The inclusion of 5% TiO2 has a great impact on the development of shielding power of D45-T5 compared with OPC; the linear attenuation coefficient (mu) values were enhanced from 0.127 +/- 0.003 cm(-1) to 0.199 +/- 0.007 cm(-1) at 661.6 Kev and from 0.118 +/- 0.003 cm(-1) to 0.144 +/- 0.005 cm(-1) at 1332.5 Kev. The unique properties of specimens containing the anatase phase may be attributed to the fact that the TiO2 may act as a nano-filler and active seeds for the formation of further hydration products such as CSHs, CAHs and CASHs as detected by X-ray diffraction (XRD), thermal analyses techniques (TGA/DSC) and scanning electron microscope (SEM/EDX). TiO2 caused rearrangement of the textural structure of D45-T5 composite to meso pores, as proved by N-2-adsorption/desorption technique. Moreover, the TiO2's tetragonal struc-ture makes it has dosimetric characteristics of high adsorbent for gamma rays

Progressive Collapse Resistance of RC Beam–Slab Substructures Made with Rubberized Concrete

Abnormal loads can produce localized damage that can eventually cause progressive collapse of the whole reinforced concrete (RC) structure. This might have devastating financial repercussions and cause numerous severe casualties. Numerical simulation, using the finite element method (FEM), of the consequences of abnormal loads on buildings is thus required to avoid the significant expenses associated with testing full-scale buildings and to save time. In this paper, FEM simulations, using ABAQUS software, were employed to investigate the progressive collapse resistance of the full-scale three-dimensional (3D) beam–slab substructures, considering two concrete mixes, namely: normal concrete (NC) and rubberized concrete (RuC) which was made by incorporating crumb rubber at 20% by volume replacement for sand. The FEM accuracy and dependability were validated using available experimental test results. Concrete and steel material non-linearity were considered in the FE modelling. The numerical study is extended to include eight new models with various specifics (a set of parameters) for further understanding of progressive collapse. Results showed that slabs contribute more than a third of the load resistance, which also significantly improves the building’s progressive collapse resistance. Moreover, the performance of the RuC specimens was excellent in the catenary stage, which develops additional resilience to significant deformation to prevent or even mitigate progressive collapse

Experimental and numerical studies of reinforced concrete stair beams strengthened with steel bars and plates

The bends under sagging moments in a Reinforced Concrete Stair Beam (RCSB) in staircases may be damaged because of improper detailing design or construction; therefore, they need to be strengthened or repaired. The structural behavior of strengthened RCSBs has not been investigated adequately. This paper presents experimental and numerical investigations on the flexural strengthening of RCSBs with bends under sagging moments. Tests on RCSBs were undertaken that were strengthened by using either the Near-Surface Mounted Steel Bars (NSMSBs) or the Externally Bonded Steel Plates (EBSPs). Three steel materials were employed, including Steel Bars (SBs), Steel Sheets (SSs) and Stainless-Steel Plates (SSPs). The test program and outcomes are described in detail of six full-scale strengthened RCSBs loaded up to collapse. A finite element model is developed employing ABAQUS to simulate the performance of the tested RCSBs. It is found that the utilized strengthening techniques effectively enhance both the cracking and ultimate loads in addition to the energy absorption capacity. The agreement between simulations and experiment is good, suggesting that the model of nonlinear finite element analysis can be used with confidence to perform further parametric instigations

Engineering Properties of High-Volume Fly Ash Modified Cement Incorporated with Bottle Glass Waste Nanoparticles

Eco-friendly sustainable construction materials with low carbon dioxide emissions and low energy consumption which utilize agricultural and industrial waste are widely recommended. Utilizing high-volume fly ash waste (FA) as a cement replacement will contribute to a reduction in the environmental problems related to cement production and landfill disposal. It is well known that the inclusion of high amounts of FA (up to 50%) as a cement replacement leads to low strength performance, especially at a concrete’s early age (below 7 days). In this study, a cement mortar with high-volume FA (60%) was developed with strength enhancement. With nanotechnology and nanomaterial benefits, nanoparticles from bottle glass waste (BGWNP) were produced and used to replace 2, 4, 6, 8, and 10% of cement–FA binder. The results showed that the compressive strength significantly improved with the inclusion of the BGWNP in a high-volume FA matrix and the strength trend increased from 21.3 to 328 MPa with increasing nanoparticle content from 0 to 6%. However, the results indicated that the inclusion of nanoparticles up to 6% led to a slight reduction in strength value. Similar trends were observed for other engineering and microstructure properties and the matrix containing 6% of BGWNP achieved the highest performance compared to that of the control sample. It is concluded that, with the utilization of BGWNP, there is an ability to produce high-volume FA-based cement with acceptable engineering properties as well as achieve sustainability goals by reducing pollution, recycling waste, and resolving landfill issues

Effect of CFRP and TRM Strengthening of RC Slabs on Punching Shear Strength

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

Rehabilitation of reinforced concrete beams subjected to torsional load using ferrocement

Recent exploration has focused on repairing and strengthen reinforced concrete (RC) beams subjected to torsional loading through various techniques. However, limited attention has been given to enhancing RC beams against torsional loading using ferrocement, resulting in inadequate evidence to illustrate its benefits. Torsional failure, a brittle and undesirable type of failure, is especially problematic in earthquake-prone regions. This paper presents an experimental study that evaluates the behavior of RC beams repaired with ferrocement when subjected to pure torsion. The study included testing six RC beams with identical cross-sectional dimensions (150 × 350 mm) and a total span of 1400 mm. The beams were divided into three segments, with a 1000 mm experimental region and two cantilever sections (200 mm wide and 350 mm long) that were extensively reinforced to prevent early failure during testing. Two primary factors were investigated: the effect of ferrocement configuration and the number of layers in the ferrocement reinforcing mesh. The tested beams provided insights into cracking, ultimate torques, rotation angles, toughness, and failure patterns. Experimental results revealed that the proposed ferrocement repair techniques unevenly enhanced the ultimate load-carrying capacity of the repaired beams, excluding U-jacket wrapping. Particularly effective was full wrapping with dual-layer wire mesh, increasing capacity by 28% compared to control beams. Using strip wrapping ferrocement with two mesh layers improved load-carrying capacity by 10% compared to control beams, while strip wrapping with one layer increased capacity by 6%. Ultimately, increasing the number of layers in the ferrocement reinforcement mesh led to an escalation in ultimate torsional capacity. This study confirms the potential of ferrocement as a strengthening method and emphasizes the significance of optimal repair configurations

Influence of aggregate source and size on the shear behavior of high strength reinforced concrete deep beams

This paper aims to examine the influence of coarse aggregate characteristics, including toughness and nominal maximum size of aggregate on the RC deep beams’ shear behavior made with and without shear reinforcement. Nine deep beams were prepared with three coarse aggregate types (i.e., limestone, steel slag, and quartzite) having different toughness properties and two nominal maximum aggregate (10 mm and 20 mm) sizes, which were examined under four-point bending. The experimental findings showed that the deep beams exhibited shear failure caused by diagonal shear cracks initiated between the supports and the loading point. Utilizing bigger coarse aggregate size has led to reducing the number of shear cracks. The deep beam stiffness was not impacted by the change in coarse aggregate toughness, aggregate size, or the use of shear reinforcement. For the beams without shear reinforcement, increasing the nominal maximum coarse aggregate size improved the deep beams normalized shear strength. This improvement depended on the coarse aggregate’s toughness with the toughest aggregate (steel slag) showing the greatest improvement. Moreover, using shear reinforcement has contributed to improving the deep beams’ normalized shear strength. The normalized shear strength increased from 6% to 16% compared to deep beams without shear reinforcement

Flexural performance of precast circular reinforced concrete members with intermediate connection filled with ultra-high-performance-concrete

Precast Reinforced concrete (RC) columns with circular sections are increasingly being utilized in the construction of RC structures. This paper reports investigations into the flexural behavior of precast circular RC members with an intermediate connection filled with Ultra-High-Performance-Concrete (UHPC). Experimental program and results are described of twelve RC circular members tested under four-point loads up to collapse. Of the twelve columns, three of them are solid ones without intermediate connection, while nine of them are precast Normal Concrete (NC) panels connected with UHPC. The studied parameters are the existence of an intermediate connection (with and without connection), the ratio of longitudinal reinforcement (µ) ratio and the length of steel bars embedded in the UHPC connection (Le). Three concrete types are used including Normal Concrete (NC), Strain Hardening Cementitious Composite (SHCC), and UHPC. Test results show that increasing the reinforcement ratio and the embedded length of the steel bars increases the strength and energy absorption of members. Finite element models (FEMs) developed using ABAQUS are presented for capturing the responses of RC columns incorporating different concrete types. The good agreement between computer simulation and experimental results suggests that the FEMs can be utilized to undertake further parametric studies with confidence

Exploration of mechanical performance, porous structure, and self-cleaning behavior for hydrothermally cured sustainable cementitious composites containing de-aluminated metakaolin waste and TiO2 nanoparticles

The main goal behind this research is to produce antimicrobial cementitious composites with acceptable mechanical characteristics based on de-aluminated metakaolin waste (DAK) and commercial titania. Two cementitious blends have been prepared: OPC containing 50%DAK and OPC containing 45%DAK +5% TiO2 NPs. Regarding curing time and cost, these blends were treated under two different curing regimes: normal curing under tap water for up to 28-days at room temperature and hydrothermal curing at various steam pressures of up to 12 bars. Compared with the reference paste (OPC/28days), compressive strength test, phases identification, morphology, textural characteristics, and microbial resistivity test were conducted. It was found that the normal cured cementitious composite containing titania NPs possessed the highest strength (88 MPa) compared with reference (80 MPa) and OPC+50%DAK (58 MPa). On the other hand, the strength value for cementitious composite modified with TiO2 NPs reached 96 MPa under autoclave curing at 4 bars for 8 h and became 61.6 MPa for OPC+50%DAK. XRD and TGA/DTG techniques confirmed the formation of binding hydrates (C-S-Hs, C-A-S-Hs and C-A-Hs) under different curing conditions. SEM/EDX indicated stacked plates, fibers, and rods of C-S-Hs under hydrothermal treatment. N2-adsorption/desorption technique revealed that autoclaving conditions significantly reduced the pore diameter of the prepared blends. Two fungi strains (Mucor-circinelloide and Aspergillus-terreus) and two bacteria strains (Gram Positive-Bacillus subtilis-ATCC6633, Gram negative-K. pneumonia-ATCC13883) were used to conduct a self-cleaning test. According to the agar diffusion test, high inhibition zones were observed for normally cured OPC-50%DAK and OPC-45%DAK-5%TiO2 pastes