Using fiber-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete columns in harsh environments has become an important method for solving corrosion problems. The brittleness of FRP bars significantly reduces the ductility of columns. It has been proposed that columns can be reinforced with hybrid FRP and steel bars to improve ductility, but related research is very limited. In this research, the axial compression behaviour of seawater sea sand concrete (SSC) columns reinforced with hybrid FRP bars and stainless steel (SS) bars was studied. In total, 84 SSC columns were designed, including 15 SS reinforced SSC (SS-SSC) columns, 15 glass-FRP (GFRP) reinforced SSC (GFRP-SSC) columns, 45 hybrid FRP-SS reinforced SSC (FRP-SS-SSC) columns and nine plain SSC columns. The failure modes, load-axial displacement curves, bearing capacity, and ductility were analyzed with consideration of the effects of the reinforcement types, reinforcement ratios, and concrete strength. The results showed that ductility could be significantly improved by hybrid reinforcements, and the ductility indexes of the FRP-SS-SSC columns were close to those of the SS-SSC columns. The proposed equation could accurately predict the bearing capacity of SSC columns Furthermore, the theoretical stress-strain relationship for the studied axial compression SSC columns was proposed.
{"title":"Axial compression behaviour of seawater sea sand concrete columns reinforced with hybrid FRP-stainless steel bars","authors":"Jinjin Xu, Zhimin Wu, H. Jia, R. Yu, Q. Cao","doi":"10.1680/jmacr.22.00249","DOIUrl":"https://doi.org/10.1680/jmacr.22.00249","url":null,"abstract":"Using fiber-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete columns in harsh environments has become an important method for solving corrosion problems. The brittleness of FRP bars significantly reduces the ductility of columns. It has been proposed that columns can be reinforced with hybrid FRP and steel bars to improve ductility, but related research is very limited. In this research, the axial compression behaviour of seawater sea sand concrete (SSC) columns reinforced with hybrid FRP bars and stainless steel (SS) bars was studied. In total, 84 SSC columns were designed, including 15 SS reinforced SSC (SS-SSC) columns, 15 glass-FRP (GFRP) reinforced SSC (GFRP-SSC) columns, 45 hybrid FRP-SS reinforced SSC (FRP-SS-SSC) columns and nine plain SSC columns. The failure modes, load-axial displacement curves, bearing capacity, and ductility were analyzed with consideration of the effects of the reinforcement types, reinforcement ratios, and concrete strength. The results showed that ductility could be significantly improved by hybrid reinforcements, and the ductility indexes of the FRP-SS-SSC columns were close to those of the SS-SSC columns. The proposed equation could accurately predict the bearing capacity of SSC columns Furthermore, the theoretical stress-strain relationship for the studied axial compression SSC columns was proposed.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46190407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lack of information regarding the shear behavior of high-strength longitudinally reinforced concrete beams without shear reinforcement (HRCBW) impedes the design engineers from using the full yield strength of material. Current shear design provisions for HRCBW were reexamined based on probability density function, confidence interval and confidence level. Based on the principal shear mechanism of beam and arch actions, a probabilistic shear capacity model for HRCBW was proposed based on the Bayesian theory and the Markov Chain Monte Carlo (MCMC) method taking into account both aleatory and epistemic uncertainties. Meanwhile, statistical characteristics (e.g. mean value, standard deviation, distribution type) of shear capacity for HRCBW were determined by Kolmogorov-Smirnov (K-S) test and statistical analysis. Moreover, the accuracy and applicability of three major shear design provisions (i.e. ACI 318-19, EC 2, fib MC2010) for HRCBW were reexamined based on probability density function, confidence interval and confidence level.
{"title":"Reexamination of shear design provisions for high-strength longitudinally RC beams","authors":"Bo Yu, Bujiu Sang, Xiaolei Tao, Bing Li","doi":"10.1680/jmacr.22.00038","DOIUrl":"https://doi.org/10.1680/jmacr.22.00038","url":null,"abstract":"Lack of information regarding the shear behavior of high-strength longitudinally reinforced concrete beams without shear reinforcement (HRCBW) impedes the design engineers from using the full yield strength of material. Current shear design provisions for HRCBW were reexamined based on probability density function, confidence interval and confidence level. Based on the principal shear mechanism of beam and arch actions, a probabilistic shear capacity model for HRCBW was proposed based on the Bayesian theory and the Markov Chain Monte Carlo (MCMC) method taking into account both aleatory and epistemic uncertainties. Meanwhile, statistical characteristics (e.g. mean value, standard deviation, distribution type) of shear capacity for HRCBW were determined by Kolmogorov-Smirnov (K-S) test and statistical analysis. Moreover, the accuracy and applicability of three major shear design provisions (i.e. ACI 318-19, EC 2, fib MC2010) for HRCBW were reexamined based on probability density function, confidence interval and confidence level.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44350136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this research, the effects of five parameters such as water to cementitious materials ratio, limestone powder, high temperatures, polypropylene and steel microfibers on the fracture energy (GF) and the critical stress intensity factor (KIC) of the notched self-compacting mortar beams were investigated. Four levels were assumed using the Taguchi method with an L16 orthogonal array for each parameter, and 32 mix designs were considered instead of 512. After the preparation of the specimens, they were placed in a furnace and exposed to three temperature levels of 200, 400, and 600 °C at a heating rate of 2 °C /min. Mortar specimens to each target temperature were kept for 6 h. As a result, the fracture properties of the specimens initially improved but then decreased after exposure to temperatures above 400 °C. At 200 °C, the density of self-compacting mortar increased and reached its maximum value, which in turn increased the fracture energy and critical stress intensity factor of the specimens at this temperature compared with those at the ambient temperature. Above this temperature up to 600 °C, increasing the temperature had destructive effects on the fracture properties. Furthermore, the reliability of the results was discussed and confirmed by using the analysis of variance.
{"title":"Fracture properties of self-compacting mortar in terms of contents and high temperatures","authors":"F. Zahedi, M. Dehestani","doi":"10.1680/jmacr.22.00157","DOIUrl":"https://doi.org/10.1680/jmacr.22.00157","url":null,"abstract":"In this research, the effects of five parameters such as water to cementitious materials ratio, limestone powder, high temperatures, polypropylene and steel microfibers on the fracture energy (GF) and the critical stress intensity factor (KIC) of the notched self-compacting mortar beams were investigated. Four levels were assumed using the Taguchi method with an L16 orthogonal array for each parameter, and 32 mix designs were considered instead of 512. After the preparation of the specimens, they were placed in a furnace and exposed to three temperature levels of 200, 400, and 600 °C at a heating rate of 2 °C /min. Mortar specimens to each target temperature were kept for 6 h. As a result, the fracture properties of the specimens initially improved but then decreased after exposure to temperatures above 400 °C. At 200 °C, the density of self-compacting mortar increased and reached its maximum value, which in turn increased the fracture energy and critical stress intensity factor of the specimens at this temperature compared with those at the ambient temperature. Above this temperature up to 600 °C, increasing the temperature had destructive effects on the fracture properties. Furthermore, the reliability of the results was discussed and confirmed by using the analysis of variance.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49475955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In reinforced concrete (RC) structural systems, the use of ultra-high performance fibre reinforced concrete (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations such as wet joints between prefabricated members. To better understand and guide construction practice of reinforced UHPFRC members, twenty-eight pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Due to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalized bond strength and residual bond strength were proposed, and an analytical model for bond stress-slip response was developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC were discussed and suggested.
{"title":"Bond behaviour of deformed reinforcing bars in ultra-high performance fibre reinforced concrete (UHPFRC)","authors":"Yang Huang, R. Zhang, Shiming Chen, P. Gu","doi":"10.1680/jmacr.22.00142","DOIUrl":"https://doi.org/10.1680/jmacr.22.00142","url":null,"abstract":"In reinforced concrete (RC) structural systems, the use of ultra-high performance fibre reinforced concrete (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations such as wet joints between prefabricated members. To better understand and guide construction practice of reinforced UHPFRC members, twenty-eight pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Due to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalized bond strength and residual bond strength were proposed, and an analytical model for bond stress-slip response was developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC were discussed and suggested.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41999984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The establishment of an aggregate model that better matches real situations is one of the prerequisites to studying the mechanical properties of concrete. Previous models have focused on aggregates with regular shapes; however, this differs from the morphology of real aggregates, particularly recycled aggregate (RA). Due to the presence of adhered mortar, RA has more complex structural characteristics than natural aggregate (NA). It is therefore difficult to model RA, especially the distributions of irregular angles and sharp corners. A new modelling method based on the compression of circles and spheres is proposed in order to obtain circular, elliptical and convex polygonal aggregates in two-dimensional (2D) models and spherical, ellipsoidal and convex polyhedral aggregates in 3D models. The compression method has excellent scalability and applies to both NA and RA in both 2D and 3D models. Using the proposed compression modelling method, the aspect ratios, sharp corners, flakes, edges and needles of RA and NA can be characterised. Random aggregate models showed that the compression modelling method was able to construct 2D and 3D geometric models of concrete made with NA and RA with desirable aggregate distributions and aggregate morphological characteristics.
{"title":"A novel numerical algorithm for 2D and 3D modelling of recycled aggregate with different geometries","authors":"Minyao Xu, Yao Wang","doi":"10.1680/jmacr.22.00214","DOIUrl":"https://doi.org/10.1680/jmacr.22.00214","url":null,"abstract":"The establishment of an aggregate model that better matches real situations is one of the prerequisites to studying the mechanical properties of concrete. Previous models have focused on aggregates with regular shapes; however, this differs from the morphology of real aggregates, particularly recycled aggregate (RA). Due to the presence of adhered mortar, RA has more complex structural characteristics than natural aggregate (NA). It is therefore difficult to model RA, especially the distributions of irregular angles and sharp corners. A new modelling method based on the compression of circles and spheres is proposed in order to obtain circular, elliptical and convex polygonal aggregates in two-dimensional (2D) models and spherical, ellipsoidal and convex polyhedral aggregates in 3D models. The compression method has excellent scalability and applies to both NA and RA in both 2D and 3D models. Using the proposed compression modelling method, the aspect ratios, sharp corners, flakes, edges and needles of RA and NA can be characterised. Random aggregate models showed that the compression modelling method was able to construct 2D and 3D geometric models of concrete made with NA and RA with desirable aggregate distributions and aggregate morphological characteristics.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47960546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Ngo, Quang-Huy Le, Duy‐Liem Nguyen, Dong Joo Kim, Ngoc-Thanh Tran
This study investigates and predicts the direct tensile resistance of strain hardening steel fiber-reinforced concrete (SHSFRC). Three steel fiber types, namely, twisted, hooked, and smooth fibers, and three matrices with different compressive strengths of 28 MPa (M1), 84 MPa (M2), and 180 MPa (M3) were investigated in both single fiber pullout tests and direct tensile tests. In addition, a machine learning-based model was developed to predict the tensile resistance of SHSFRC. The experimental results showed that twisted fibers exhibited not only the highest pullout resistance but also the greatest tensile resistance in M1 and M2, whereas smooth fibers achieved the same results in M3. From the predicting outcomes, the proposed model achieved high efficiency and accuracy in estimating the tensile resistance of SHSFRC, with a correlation coefficient of 0.951.
{"title":"Experiments and prediction of direct tensile resistance of strain hardening fiber-reinforced concrete","authors":"T. Ngo, Quang-Huy Le, Duy‐Liem Nguyen, Dong Joo Kim, Ngoc-Thanh Tran","doi":"10.1680/jmacr.22.00060","DOIUrl":"https://doi.org/10.1680/jmacr.22.00060","url":null,"abstract":"This study investigates and predicts the direct tensile resistance of strain hardening steel fiber-reinforced concrete (SHSFRC). Three steel fiber types, namely, twisted, hooked, and smooth fibers, and three matrices with different compressive strengths of 28 MPa (M1), 84 MPa (M2), and 180 MPa (M3) were investigated in both single fiber pullout tests and direct tensile tests. In addition, a machine learning-based model was developed to predict the tensile resistance of SHSFRC. The experimental results showed that twisted fibers exhibited not only the highest pullout resistance but also the greatest tensile resistance in M1 and M2, whereas smooth fibers achieved the same results in M3. From the predicting outcomes, the proposed model achieved high efficiency and accuracy in estimating the tensile resistance of SHSFRC, with a correlation coefficient of 0.951.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46937745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mobilisation of alternate load path (ALP) mechanisms in 3D beam-slab systems is a key factor in designing structures against progressive collapse. Existing analytical methods on 3D beam-slab systems focusing on limited load-resisting mechanisms often lead to uneconomical and unrealistic design, while finite element models with 3D solid elements are too complicated and time consuming for 3D beam-slab systems. To address these shortcomings, this paper aims to provide structural engineers two simple but effective and reliable approaches to predict structural behaviour of 3D beam-slab systems. They include (i) an analytical method and (ii) a simplified finite element model based on strip method and grillage analysis. Both approaches are validated against published test results for 3D beam-slab systems. Compared to existing approaches on 3D beam-slab systems, these two proposed methods incorporate all the load resisting mechanisms in both the beams and slabs, giving more accurate and realistic predictions of load-displacement curves for the sub-structures considered. In addition, parametric studies on the analytical approach are presented to shed light on the role of boundary conditions and the contribution of slabs to load resistance capacity of 3D beam-slab structures against progressive collapse.
{"title":"Structural assessment on beam-slab reinforced concrete sub-structures under column loss scenario","authors":"Manh Ha Tran, K. Tan","doi":"10.1680/jmacr.22.00186","DOIUrl":"https://doi.org/10.1680/jmacr.22.00186","url":null,"abstract":"Mobilisation of alternate load path (ALP) mechanisms in 3D beam-slab systems is a key factor in designing structures against progressive collapse. Existing analytical methods on 3D beam-slab systems focusing on limited load-resisting mechanisms often lead to uneconomical and unrealistic design, while finite element models with 3D solid elements are too complicated and time consuming for 3D beam-slab systems. To address these shortcomings, this paper aims to provide structural engineers two simple but effective and reliable approaches to predict structural behaviour of 3D beam-slab systems. They include (i) an analytical method and (ii) a simplified finite element model based on strip method and grillage analysis. Both approaches are validated against published test results for 3D beam-slab systems. Compared to existing approaches on 3D beam-slab systems, these two proposed methods incorporate all the load resisting mechanisms in both the beams and slabs, giving more accurate and realistic predictions of load-displacement curves for the sub-structures considered. In addition, parametric studies on the analytical approach are presented to shed light on the role of boundary conditions and the contribution of slabs to load resistance capacity of 3D beam-slab structures against progressive collapse.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2023-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42448414","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Structures are exposed to various external effects and loads throughout their service life. Such a case then results in failure at a load lower than the design compressive strength. Although there is a cement-based healing system for repairing these damages, it is often insufficient. Therefore, a more effective autonomous healing system is needed, and microbial-induced calcite precipitation (MICP) was most of the time experimented with for this purpose. In this study, bacterial mortar samples were produced and loaded at different levels of their ultimate compressive stress. The effects of the loads were determined, and the effectiveness of bacterial treatments was also investigated. Crack healing, compressive strength, water absorption, ultrasonic pulse velocity (UPV), and high temperature effect experiments were conducted. In bacterial mortar samples, the MICP mechanism repaired about 3.5 times larger cracks than the control samples. While the treatment of cracks and damage observed at 90% and 100% loading levels were highly limited thanks to the autogenous system, some properties of bacterial mortars improved as the loading level increased. It was observed that the MICP mechanism was more effective, especially in damaged samples with high load levels. In addition, bacterial mortars demonstrated more advanced physical, mechanical, and durability properties at each loading level.
{"title":"Bacteria based self-healing of cement mortars loaded at different levels and exposed to high temperature","authors":"M. Yıldırım, Hacer Bilir Özhan, Hilal Girgin Öz","doi":"10.1680/jmacr.22.00238","DOIUrl":"https://doi.org/10.1680/jmacr.22.00238","url":null,"abstract":"Structures are exposed to various external effects and loads throughout their service life. Such a case then results in failure at a load lower than the design compressive strength. Although there is a cement-based healing system for repairing these damages, it is often insufficient. Therefore, a more effective autonomous healing system is needed, and microbial-induced calcite precipitation (MICP) was most of the time experimented with for this purpose. In this study, bacterial mortar samples were produced and loaded at different levels of their ultimate compressive stress. The effects of the loads were determined, and the effectiveness of bacterial treatments was also investigated. Crack healing, compressive strength, water absorption, ultrasonic pulse velocity (UPV), and high temperature effect experiments were conducted. In bacterial mortar samples, the MICP mechanism repaired about 3.5 times larger cracks than the control samples. While the treatment of cracks and damage observed at 90% and 100% loading levels were highly limited thanks to the autogenous system, some properties of bacterial mortars improved as the loading level increased. It was observed that the MICP mechanism was more effective, especially in damaged samples with high load levels. In addition, bacterial mortars demonstrated more advanced physical, mechanical, and durability properties at each loading level.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2022-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47790525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mohammadreza Hajiaghamemar, D. Mostofinejad, H. Bahmani
The use of engineered cementitious composite (ECC) is increasing due to its high tensile strength and ductility, however, little attention has been paid to substitutes for its ingredients. Blast furnace slag instead of fly ash and polypropylene (PP) fibres instead of polyvinyl alcohol (PVA) fibres may be considered to be appropriate alternative substitutes. However, scanty research has examined the effect of using high levels of slag and PP fibres on the mechanical properties and microstructure of ECC. Therefore, the present study aimed to produce an engineered cementitious composite with a large proportion of slag and PP fibres for achieving high strength and ductility characteristics and creating a controlled microcracking behavior under tensile stresses (i.e., strain-hardening behavior). The specimens made from the ECC thus prepared were subjected to compressive, four-point flexural, X-ray diffraction assessment (XRD), and scanning electron microscope (SEM) tests. The results showed that the slag-to-cement ratio of 0.5 in ECC led to the highest compressive strength (55.6 MPa) and modulus of rupture (7.0 MPa), while the corresponding energy absorption was fairly high. The results of XRD and SEM analyses indicated that applying the slag-to-cement ratio of 0.5 led to a homogenous cement matrix and produced the highest calcium-silicate-hydrate (C-S-H) in the ECC microstructure. Finally, to predict the load-deflection of specimens, a three-part model was proposed and verified with other available data.
{"title":"High volume of slag and PP fibres in engineered cementitious composites (ECC): Microstructure and mechanical properties","authors":"Mohammadreza Hajiaghamemar, D. Mostofinejad, H. Bahmani","doi":"10.1680/jmacr.22.00128","DOIUrl":"https://doi.org/10.1680/jmacr.22.00128","url":null,"abstract":"The use of engineered cementitious composite (ECC) is increasing due to its high tensile strength and ductility, however, little attention has been paid to substitutes for its ingredients. Blast furnace slag instead of fly ash and polypropylene (PP) fibres instead of polyvinyl alcohol (PVA) fibres may be considered to be appropriate alternative substitutes. However, scanty research has examined the effect of using high levels of slag and PP fibres on the mechanical properties and microstructure of ECC. Therefore, the present study aimed to produce an engineered cementitious composite with a large proportion of slag and PP fibres for achieving high strength and ductility characteristics and creating a controlled microcracking behavior under tensile stresses (i.e., strain-hardening behavior). The specimens made from the ECC thus prepared were subjected to compressive, four-point flexural, X-ray diffraction assessment (XRD), and scanning electron microscope (SEM) tests. The results showed that the slag-to-cement ratio of 0.5 in ECC led to the highest compressive strength (55.6 MPa) and modulus of rupture (7.0 MPa), while the corresponding energy absorption was fairly high. The results of XRD and SEM analyses indicated that applying the slag-to-cement ratio of 0.5 led to a homogenous cement matrix and produced the highest calcium-silicate-hydrate (C-S-H) in the ECC microstructure. Finally, to predict the load-deflection of specimens, a three-part model was proposed and verified with other available data.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44038508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In response to the shortcomings of traditional concrete crack repair materials, a new generation of repair materials has been developed - a microbial repair material based on sodium alginate modification. The method adopts a brushing technique to fix the microorganisms on the cracks to be repaired so that they can deposit calcium carbonate in situ to repair the cracks. This paper carried out a study of the fundamental properties of the repair material, as well as studied the macroscopic morphology and surface water absorption of its specimens before and after repairing mortar cracks, and analyzed the material changes and microstructures of the repair products. The results showed that: (1) the CaCO3 content, water absorption ratio and heating shrinkage rate of the microbial repair material modified with sodium alginate were better than those of the repair material without microorganisms; (2) the microorganisms were fixed in the cracks on the surface of the mortar using the brushing technique with sodium alginate as the carrier and were able to adhere tightly to the cracks after only two repairs to produce repair products, which were mainly calcium alginate and calcium carbonate, and the surface water absorption rate was reduced by about 65% compared to that before the repair.
{"title":"Effect of microbial repair materials based on sodium alginate modification on mortar crack repair","authors":"Kaiyue Hu, H. Rong, Ye Shi, G. Ma, Xinguo Zheng","doi":"10.1680/jmacr.22.00237","DOIUrl":"https://doi.org/10.1680/jmacr.22.00237","url":null,"abstract":"In response to the shortcomings of traditional concrete crack repair materials, a new generation of repair materials has been developed - a microbial repair material based on sodium alginate modification. The method adopts a brushing technique to fix the microorganisms on the cracks to be repaired so that they can deposit calcium carbonate in situ to repair the cracks. This paper carried out a study of the fundamental properties of the repair material, as well as studied the macroscopic morphology and surface water absorption of its specimens before and after repairing mortar cracks, and analyzed the material changes and microstructures of the repair products. The results showed that: (1) the CaCO3 content, water absorption ratio and heating shrinkage rate of the microbial repair material modified with sodium alginate were better than those of the repair material without microorganisms; (2) the microorganisms were fixed in the cracks on the surface of the mortar using the brushing technique with sodium alginate as the carrier and were able to adhere tightly to the cracks after only two repairs to produce repair products, which were mainly calcium alginate and calcium carbonate, and the surface water absorption rate was reduced by about 65% compared to that before the repair.","PeriodicalId":18113,"journal":{"name":"Magazine of Concrete Research","volume":"1 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67489037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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