CONSTRUCTION AND BUILDING MATERIALS (Elsevier Ltd.)
A novel casting procedure for SFRC piles without shear reinforcement using the centrifugal forming technique to manipulate the fiber orientation and distribution
Raju, R.A., Akiyama, M., Lim, S., Kakegawa, T., Hosono, Y.
CONSTRUCTION AND BUILDING MATERIALS, Vol.303, 2021, OCT.
(https://doi.org/10.1016/j.conbuildmat.2021.124232)
Abstract
The structural performance of steel fiber-reinforced concrete (SFRC) members primarily depends on the distribution and orientation of the fibers. Previous experimental studies revealed that the distribution and orientation of fibers are random and hardly controlled during the fabrication process. The centrifugal forming technique may improve the orientation and distribution of steel fibers in hollow circular SFRC piles and increase the shear strength of the piles. Accomplishing this task can lead to the possible replacement of shear reinforcements with steel fibers in piles, thereby improving the demanding productivity that is desired in the pile construction industry by saving considerable time and labor. This paper presents a novel experimental program to (a) develop the casting procedure for SFRC piles and (b) investigate the shear strength of SFRC piles without shear reinforcement compared to that of conventional reinforced concrete (RC) piles with shear reinforcement. With the aid of X-ray technology, different mix proportions and casting methods were investigated to determine the optimum procedure, which produced fiber distributions and orientations in SFRC piles superior to those of RC piles. The centrifugal forming method influenced the orientation of the fibers so that they were oriented in the shear stress direction (i.e., circumferential direction). The loading test demonstrated that the steel fibers effectively worked as shear reinforcement and that the shear capacity increased with the steel fiber content. Moreover, the SFRC piles exhibited stable crack propagation and improved post-cracking stiffness without severe concrete damage compared to that of the RC piles.
Experimental study on the porosity evaluation of pervious concrete by using ultrasonic wave testing on surfaces
E, R., Hatanaka, S., Palamy, P., Kurita, S.
CONSTRUCTION AND BUILDING MATERIALS, Vol.300, 2021, SEP.
(https://doi.org/10.1016/j.conbuildmat.2021.123959)
Abstract
This research conducts two experiments (Experiments I and II) to determine methods for estimating the porosity of pervious concrete (PC) using ultrasonic wave testing. In Experiment I, the ultrasonic wave propagation on the PC surface (surface method), which can be applied during onsite PC construction, was focused on estimating the porosity of PC and the testing method itself. In Experiment II, the effect of specimen thickness on the ultrasonic wave velocity of PC was investigated. Results deduced that the quantitative relationship between ultrasonic wave velocity and PC porosity can be approximated by a quadratic function. It was confirmed that the ultrasonic wave velocity (surface method) was not affected by the thickness of the PC specimen. Therefore, as a conclusion from the results, the porosity of onsite PC construction may be estimated by using the measured ultrasonic wave velocity (surface method) according to the procedure proposed in this article (see Fig. 19 in the article in detail for the porosity estimating procedure).
Experimental study on bond behavior of corroded rebars coated by anti-corrosive materials in polymer cement mortar
Natino, M.R.L., Yang, Y., Nakamura, H., Miura, T.
CONSTRUCTION AND BUILDING MATERIALS, Vol.300, 2021, SEP.
(https://doi.org/10.1016/j.conbuildmat.2021.124228)
Abstract
This study investigates the bond behavior of anti-corrosive coated corroded rebars in a polymer cement mortar (PCM) as a common patching material to repair corrosion-induced damaged reinforced concrete structures. Cementitious and epoxy types of anti-corrosive coating materials are utilized. The corroded rebars are prepared by accelerated corrosion test in laboratory with a 5?10% target corrosion degree. The single effect of the coating materials on the bond behavior is investigated using coated round and deformed rebars. The combined effects of the corrosion and the coating materials are investigated using coated corroded deformed rebars. To thoroughly understand the bond behavior and mechanism, the effects of the corrosion and the coating materials on the change in the geometrical properties and surface roughness of the rebars are quantitatively analyzed by laser scanning tests. Finally, a two-end pull-out test is conducted to measure and investigate the bond-slip relationship, ultimate bond strength, bond toughness, and bond ductility.
Similar to the findings on cementitious coated deformed rebar confined in concrete in a previous study by the authors, the results of the current study revealed that in the PCM, the cementitious coated rebar presents promising good bond performance regardless of the corrosion degree compared to the epoxy coated rebar. This is because when the ribs of the deformed rebars would deteriorate owing to corrosion, the rough surface of a cementitious coated rebar can sustain well its bond performance compared with the smooth and glassy surface of an epoxy coated rebar. Moreover, the direct effect of the surface roughness characteristics of these coating materials is clarified using coated round rebars. Consequently, the cementitious coated rebar achieves a considerably higher bond strength with a brittle behavior than the epoxy coated rebar, which presents a ductile behavior.
Cost-effective system for detection and quantification of concrete surface cracks by combination of convolutional neural network and image processing techniques
Miao, P., Srimahachota, T.
CONSTRUCTION AND BUILDING MATERIALS, Vol.293, 2021, JUL.
(https://doi.org/10.1016/j.conbuildmat.2021.123549)
Abstract
This study proposed a semi-automated system for crack detection and quantification, based on the combination of a trained convolutional neural network (CNN) and a developed application. Specifically, we tested four commonly used CNNs and determined GoogLeNet for this study. Then, the transfer learning and fully training of GoogLeNet were further tested on our testing dataset and a public dataset. The results show that the transfer learning GoogLeNet has relatively balanced performances on these two datasets, with accuracy of 96.69% and 88.39%, respectively. A new sliding window technique (neighborhood scanning) was proposed and shown almost equivalent performance to the previous dual scanning method. A method for calculating crack width was presented. The average relative error of this method is 14.58% (0.05 mm), i.e., much smaller than the 36.37% (i.e., 0.14 mm) of the previous method. An application was then developed to integrate the proposed methods and other techniques such as edge detectors, boundary tracking, and threshold segmentation to segment, quantify, and analyze cracks. Verifications on 23 untrained raw images (eleven with 10240 × 2048 pixels, twelve with 2592 × 4608 pixels) show that: (1) the developed system and a previous pixel-level segmentation system require an average of 9.48 s and 10.35 s; (2) these two systems show an 80.40% and a 78.64% average Intersection over Union (IoU). Therefore, the proposed system is a cost-effective solution for detecting and analyzing cracks on concrete surfaces considering its practical performance and time cost. Practically, the proposed system could be used to analyze the images collected from onsite inspection or from experiment.
Latin Hypercube Sensitivity Analysis and Non-destructive Test to Evaluate the Pull-out Strength of Steel Anchor Bolts Embedded in Concrete
Saleem, M., Hosoda, A.
CONSTRUCTION AND BUILDING MATERIALS, Vol.290, 2021, JUL.
(https://doi.org/10.1016/j.conbuildmat.2021.123256)
Abstract
Anchor bolts are extensively employed in the various industries such as construction, mechanical and mining. Their applications range from installing permanent objects such as hybrid structures, lighting piles, direction signs to structures installed for serving temporary purpose. Several destructive testing methods have been proposed to investigate the pull-out strength of anchor bolts. However, the first real non-destructive testing method that used Schmidt hammer rebound number to estimate the load carrying capacity of anchor bolts was successfully proposed by the authors. In this method the authors successfully relate the pull-out strength of the steel anchors, N, embedded in the concrete with the Schmidt hammer rebound number, R. The research team was successful in identifying anchor bolts with improper installation resulting in lower pull-out strength. It was observed during experimentation that strength of steel anchor bolts depends upon several factors such as concrete strength, embedment length, bolt diameter, its alignment and rebound number. The cut-off value, R, of 56, 61 was identified for steel anchors of 8 mm, 10 mm diameters with embedment lengths of 50 mm and the R value of 55, 53 and 51 was identified as cut-off for 12 mm, 16 mm and 20 mm diameters with embedment lengths of 50 mm and 70 mm, respectively. Anchors depicting higher rebound values can be considered as properly installed while anchors with lower rebound value indicate defects in installation and quality of surrounding concrete. Furthermore, a detailed random parametric analysis employing Latin Hypercube Sampling method to conduct sensitivity analysis of 144 anchor bolts test data. Five diameter anchor bolts with two embedment depths were tested and analyzed. Through the analysis of experimental data, the influence of each parameter was investigated in order to ascertain its impact on the load carrying capacity of the anchor bolts. It is confirmed that the alignment of the anchor bolt is most dominant factor among all random factors considered in the analysis. Furthermore, the embedment length holds a larger influence on the pull-out strength as compared to the bolt diameter.
Investigation on the fast carbon dioxide sequestration speed of cement-based materials at 300 °C–700 °C
Wang, D., Noguchi, T., Nozaki, T., Higo, Y.
CONSTRUCTION AND BUILDING MATERIALS, Vol.291, 2021, JUL.
(https://doi.org/10.1016/j.conbuildmat.2021.123392)
Abstract
In recent years, the increasing global temperature, caused by excessive carbon dioxide emission, has put a significant threat on the earth‘s environment. Therefore, the development of fast carbon dioxide sequestration technologies is urgently needed. In this study, a high-temperature carbonation technique has been proposed by using cement-based materials. The carbon dioxide sequestration efficiencies of cement paste were tested and evaluated from 300 °C to 700 °C, exhibiting different characteristics compared with that at ambient temperature, with optimum carbonation temperature at 600 °C. The operating parameters, such as carbonation time, sample size, vapor content, and water to cement ratio, which play a significant role in the carbonation reaction, have also been investigated and compared with that at ambient temperature. It was found that the high efficiency of carbon dioxide sequestration could be achieved in the samples with large size and low water to cement ratio.
Hydration of ferrite-rich Portland cement: Evaluation of Fe-hydrates and Fe uptake in calcium-silicate-hydrates
Noguchi, N., Siventhirarajah, K., Chabayashi, T., Kato, H., Nawa, T., Elakneswaran, Y.
CONSTRUCTION AND BUILDING MATERIALS, Vol.288, 2021, JUN.
(https://doi.org/10.1016/j.conbuildmat.2021.123142)
Abstract
The hydration process in ferrite-rich cement (FC) and its pore structure have been investigated by experimental and thermodynamic modelling techniques. X-ray diffraction (XRD)/Rietveld analysis, thermogravimetry (TG), and mercury intrusion porosimetry (MIP) were performed to study the hydration process, pore volume-pore size distributions, and Fe uptake in calcium-silicate-hydrate (C-S-H). Similar phases were found in both FC and ordinary Portland cement (OPC). The hydration degree of FC was higher at the early stage compared with that of OPC; however, the hydration of OPC exceeded that of FC after 14?days because the high amount of C2S in OPC promoted the late hydration. The XRD-TG results revealed relatively similar Fe uptake by C-S-H in both FC and OPC. The thermodynamic model confirmed the formation of a high amount of Fe phases in FC. Moreover, the model predictions agreed well with the experimental results, demonstrating the accuracy of the proposed model for FC.
Investigation of the effects of multiple and multi-directional reinforcement on corrosion-induced concrete cracking pattern
Hafiza, FZ; Punyawut, J; Vikas, S, Kuntal; Nagai, K
CONSTRUCTION AND BUILDING MATERIALS, Vol.283, 2021, MAY.
(https://doi.org/10.1016/j.conbuildmat.2021.122594)
Abstract
Reinforced concrete (RC) structures are widely used, yet prone to damage induced by reinforcement corrosion which causes susceptibility of concrete spalling and eventually a reduced serviceable life. The visual inspection has been performed usually for structural assessment, but this does not account for the local interactions between rebars. Consequently, detailed scrutiny is required to consider the effects of various parameters on the initiation and propagation of corrosion-induced cracking. This experimental study considers the effect of multiple and multidirectional rebars on the development of corrosion cracking. Additionally, the effect of the location of corrosion and the change in order of corrosion occurrence is investigated in this research. For this purpose, reinforced concrete panels with unidirectional and multidirectional rebar arrangements and varying cover depth are tested using an accelerated corrosion technique. The results show a significant role of confinement in controlling the widths of cracks provided by both reinforcement arrangements. Moreover, the effect of boundary conditions along with increased confining pressure alters the generation of cracks in a unidirectional reinforcement arrangement. In the absence of enough surrounding concrete, cracks along non-corroding rebars can also form because of the expansion of adjacent corroding rebars. The inclusion of multidirectional reinforcement alters the crack direction and causes cracking along non-corroding rebars. Further, previously generated cracks may close considerably by the pressure from adjacent rebar corrosion. This study also facilitates the comprehension of the impact of influencing factors affecting corrosion cracking in real structures.
Diffusion of chloride ion in coral aggregate seawater concrete under marine environment
Wang, G., Wu, Q., Zhou, H., Peng, C., Chen, W.
CONSTRUCTION AND BUILDING MATERIALS, Vol.284, 2021, MAY.
(https://doi.org/10.1016/j.conbuildmat.2021.122821)
Abstract
In this study, the diffusion law of chloride ion in coral aggregate seawater concrete (CASC) (strength = C30) was investigated in order to determine the time-varying law of chloride ion migration and penetration in CASC under two different marine environments (i.e. immersion and wet/dry cycles). By measuring the free chloride ion concentration (Cf) and apparent chloride ion concentration (Cs) in CASC at different erosion times, erosion modes and erosion depths, the chloride ion diffusion coefficient (D) was determined, and then the chloride ion diffusion model of CASC was developed. Combined with COMSOL finite element simulation software, the chloride ion transport model was verified and improved. The results show that the diffusion law of chloride ions in the two environments conforms to Fick's second law of diffusion, and there was a significant promotional effect on the diffusion of chloride ions for the CASC in the wet/dry cycles environment; the trends of Cs and D are consistent with time and conform to the power function relationship. The value of Cf calculated by using COMSOL has good correlation with the test results; the curve shape of the numerical data is consistent with the test data, and numerical error is very small, which verifies the accuracy of the model developed in this study.
AE source location of debonding steel-rod inserted and adhered inside rubber
Kawasaki, Y; Ueda, K; Izuno, K
CONSTRUCTION AND BUILDING MATERIALS, Vol.279, 2021, APR 12.
(https://doi.org/10.1016/j.conbuildmat.2021.122383)
Abstract
Rubber bearings have been applied worldwide to bridge and building components. However, it comes out a critical issue, since significant amounts of damage and deterioration of the bearings have been reported. Therefore, the authors attempted an experimental study on damage evaluation of rubber bearings, by using acoustic emission (AE) method. In the case, it was found that the velocity of the elastic-wave propagating inside the rubber was slower than those of concrete, steel, and other rigid materials. As a result, one question remains on the location accuracy, where AE sources are generated inside the rubber. In order to clarify an applicability of AE method to damage evaluation of rubber bearings, experimental research was conducted. A steel rod was inserted in a rubber specimen and the tip of the rod was adhered. Then, debonding of the rod was measured with a pull-out test. Even distances from the tip of the steel rod to the rubber surface were investigated. Two types of AE sensors were used, with resonances at 60 kHz and 150 kHz. A three-dimensional location analysis was performed by AE method to identify debonded locations. Thus, both applicability and accuracy of AE method in the rubber bearings are verified, and a good promise to evaluate the damage in the rubber bearings is confirmed.
A study on spalling behaviour of geopolymer mortars using ring restraint test
Ozawa, M; Shaikh, FUA
CONSTRUCTION AND BUILDING MATERIALS, Vol.279, 2021, APR 12.
(https://doi.org/10.1016/j.conbuildmat.2021.122494)
Abstract
This paper presents the spalling behaviour of two types of geopolymer mortars (fly ash geopolymer and fly ash-slag geopolymer) using ring restraint specimens and is compared with normal cement mortar and polymer cement mortar. All mortar specimens are exposed to fire according to RABT 30 fire curve. Spalling depth, area and volume of all mortar specimens are measured to grade the spalling performance according to Japan Concrete Institute (JCI) spalling evaluation guide. Restraint stress, vapour pressure and temperatures at various depths from heated surface of all mortar specimens are also measured to evaluate the spalling behaviour. Results show that the fly ash-slag geopolymer mortar, normal cement mortar and polymer cement mortar spall compared to no spalling of fly ash geopolymer mortar. However, micro cracking is observed on the heated surface of fly ash geopolymer mortar specimen. Among the three mortars which showed spalling, the fly ash-slag geopolymer mortar took longer time to spall. The moisture content of both geopolymer mortars is lower than that of normal cement mortar and polymer cement mortar and this might be the reason for better spalling behaviour of former than that of latter mortars. Based on JCI spalling evaluation criteria the fly ash geopolymer mortar exhibited much better performance than the other mortars. Sharp increase in vapour pressure and sudden drop of vapour pressure are observed in all three mortar specimens which showed spalling behaviour, except the fly ash geopolymer mortar where no such sudden drop in vapour pressure is observed.
Effects of chloride ions on the durability and mechanical properties of sea sand concrete incorporating supplementary cementitious materials under an accelerated carbonation condition
Dang, VQ; Ogawa, Y; Bui, PT; Kawai, K
CONSTRUCTION AND BUILDING MATERIALS, Vol.274, 2021, MAR 8.
(https://doi.org/10.1016/j.conbuildmat.2020.122016)
Abstract
The aim of this study is to investigate the effects of chloride ions on the durability and mechanical properties of non-desalted sea sand (NSS) concrete containing fly ash (FA) or ground granulated blast furnace slag (BFS) under accelerated carbonation. Six mixtures were prepared using a constant water-to-cementitious materials ratio of 0.50. The cementitious materials consisted of primarily ordinary Portland cement with a portion replaced by a supplementary material, either FA (15% by mass) or BFS (45% by mass). After being cured with a sealed condition of 20 degrees C for 28 days, half of the concrete specimens remained sealed while the other half were exposed to an accelerated carbonation chamber for 182 days. The accelerated carbonation chamber consisted of a 5% CO2 concentration with 60% relative humidity. The durability and mechanical properties of the concrete were investigated, including carbonation resistance, sorptivity, compressive strength, and the modulus of elasticity. The chloride binding capacity was also evaluated. Porosity, crack evaluation, and scanning electron microscopy tests were implemented to better understand the macro- and microscopic structures of the different concrete compositions. The results showed that the presence of chloride ions in NSS could improve the carbonation resistance of concrete. Carbonation shrinkage generated cracks which led to a significant increase in sorptivity for the FA and BFS concretes under accelerated carbonation. However, this increase was restricted by the chloride ions in NSS. In general, the presence of chloride ions enhanced the mechanical properties of the concrete, regardless of curing ages, FA or BFS replacement, or exposure conditions. Even considering the effects of carbonation, NSS is found to be potentially viable material for use in concrete production.
Effects of frost-damaged reinforced concrete beams on their impact resistance behavior
Kurihashi, Y; Konno, H; Hama, Y
CONSTRUCTION AND BUILDING MATERIALS, Vol.274, 2021, MAR 8.
(https://doi.org/10.1016/j.conbuildmat.2020.122089)
Abstract
Impact loading experiments were conducted to clarify the impact resistance behavior of frost-damaged reinforced concrete (RC) beams. The load-bearing performance and their response deflections were evaluated based on the energy conservation concept. The experimental results indicated that 1) when frost deterioration occurred on the top face, the compressive failure of the top concrete was significant; and the response deflection increased, and 2) when frost deterioration occurred at the bottom face, the response waveform was almost identical to that generated when no deterioration occurred; however, the bottom cover concrete peeled off during elastic stress wave propagation.
Experimental study on the effect of anti-corrosive coatings on bond behavior of corroded rebar
Natino, MRL; Yang, YZ; Nakamura, H; Miura, T
CONSTRUCTION AND BUILDING MATERIALS, Vol.274, 2021, MAR 8.
(https://doi.org/10.1016/j.conbuildmat.2020.121716)
Abstract
This research presents the investigation of the effect of anti-corrosive coatings on the bond behavior of corroded rebar to concrete. Cementitious and epoxy types of anti-corrosive coating materials have been considered and applied manually to rebar as the actual on-site repair procedure of corrosion-induced damaged reinforced concrete (RC) structure. Test specimens prepared were served to investigate the direct effect of coating materials and their combined effects with corrosion. Accelerated electric corrosion test was employed with a target degree of corrosion ranging from 5 to 10%. Laser scanning test was conducted to evaluate and quantify the changed on geometrical properties and surface roughness condition of the sound-coated, bare corroded, and corroded-coated rebar specimens. Finally, two end pull-out tests were conducted to measure the bond-slip relationship, ultimate bond strength, bond toughness and bond ductility. As an important finding, the anti-corrosive coating materials had a significant effect on the change of geometrical properties and surface roughness condition of deformed rebar that have a direct effect on bond behavior and mechanism. Cementitious coating compromised the relative rib area of rebar but enhanced its surface roughness, while epoxy coating maintained the relative rib area of rebar but compromised its surface roughness. Consequently, cementitious coated rebars provide the good bond performance regardless of corrosion degree compared to epoxy coated rebars.
Experimental study on grout defects detection for grouted splice sleeve connectors using stress wave measurement
Xu, B; Fan, XL; Wang, HD; Zhou, SJ; Wang, C; Chen, HB; Ge, HB
CONSTRUCTION AND BUILDING MATERIALS, Vol.274, 2021, MAR 8.
(https://doi.org/10.1016/j.conbuildmat.2020.121755)
Abstract
Grouted splice sleeve (GSS) connectors have been widely employed to connect rebars in prefabricated concrete (PC) structures. However, grout defects may occur due to manual operation miss or poor control approaches for quality, which weaken the efficient embedment of rebars in GSS connectors and lead to a negative effect on mechanical properties of PC structures. The development of reliable and efficient grout defect detection methods for GSS connectors is challenging because its inaccessibility and inner structure complexity. In this paper, an active grout defects detection approach for GSS connectors using direct stress wave measurement is proposed, where piezoelectric-lead-zirconate-titanate (PZT) patches are mounted on the surface of the sleeve as actuators and sensors, and experimental study is carried out to validate its feasibility. Stress wave propagating along the GSS connectors excited by the surface-mounted PZT actuator is measured with PZT sensors. In order to investigate the effect of grout defects on stress wave measurement, four GSS specimens with different degrees of mimicked grout defects are designed and analysis on the PZT sensor measurement with a pitch and catch pattern is carried out. By comparing the PZT sensors measurement of different specimens without and with different grout defects under an identical impulse excitation signal, the grout defect is detected. The relationship between a normalized defect evaluation index (DEI) determined by the use of the PZT sensor measurement and the grout defect severity is analyzed. Experimental results indicate grout defect leads to increase in PZT sensors measurement compared with that of specimen without grout defect. The results show that the proposed approach based on stress wave measurement is efficient in detecting grout defect and the stress wave measurement is sensitive to the dimension of grout defect in GSS.
The applicability of SPH and MPS methods to numerical flow simulation of fresh cementitious materials
Xu, ZS; Li, ZG; Jiang, F
CONSTRUCTION AND BUILDING MATERIALS, Vol.274, 2021, MAR 8.
(https://doi.org/10.1016/j.conbuildmat.2020.121736)
Abstract
This paper aims to clarify applicability of two variants of SPH and MPS methods, namely, a weakly compressible SPH (WCSPH) and a completely implicit MPS (I-MPS) to the flow simulation of freshly mixed cementitious materials (FCM). By comparing the numerical and experimental results of L-flow of fresh mortars, it is found that the I-MPS method has higher calculation efficiency and accuracy. The applicability of the WCSPH method to the gravity-induced flow simulation of FCM is dependent on its fluidity and initial height, whereas the I-MPS method has wide application range if the boundary slippage resistance is appropriately considered. In case of fresh mortar, the I-MPS simulations, using Bingham model and VGM (Viscous Granular Material) model, has almost the same accuracy when the mortar is subjected to a high pressure, whereas the VGM model has high accuracy in case of low pressure. When a large gravity-induced pressure or a large external force acts on FCM, the WCSPH calculates greatly fluctuating inter-particle pressures, while the I-MPS method yields very stable and precise inter-particle pressures.
Critical amount of corrosion and failure behavior of flexural reinforced concrete beams
Hansapinyo, C; Vimonsatit, V; Matsushima, M; Limkatanyu, S
CONSTRUCTION AND BUILDING MATERIALS, Vol.270, 2021, FEB 8.
(https://doi.org/10.1016/j.conbuildmat.2020.121448)
Abstract
Offshore structures are subjected to chloride ion penetration leading to corrosion of the embedded steel rebars. A tensile steel bar with non-uniform corrosion such as pitting can rupture prior to yielding. In this study, the critical corrosion amount that causes tensile steel rupture in reinforced concrete beams was determined in two parts of work. In the first part, the flexural performance of low-to-highly corroded reinforced concrete beam was investigated. A series of load tests comprising of 44 reinforced concrete specimens, all having a rectangular section, 80 mm wide by 120 mm deep, and the length of 550 mm, were conducted. Each beam was reinforced with one D10 steel bar as the tension reinforcement, one acrylic top reinforcement and sufficient shear reinforcement to avoid shear failure mode. The corrosion in the steel bars was induced with an electrolytic set up with the controlled amount based on Faraday's law. These bars were extracted from the beams to measure the actual corrosion amount after the test. The results show a sharp reduction in the ultimate load and ductility when the corrosion was over 30%, and concrete crushing was observed at failure. In the second part of the work, tension tests of 17 D10 bars with 0-15% corrosions were carried out to investigate the rupture strain of the bars. The test results show the exponential decay function of the rupture strain as the corrosion increases. The obtained decay function was then used in determining the bending capacity and the failure mode of RC beams. Based on the calculation, the critical amount of corrosion altering the failure mode from yielding to rupture was 15%. Moreover, to reflect uncertainties in the natural process of the corrosion, the variation of the corrosion amount due to the pitting behavior and the rupture strain with the obtained standard deviations of the test data were considered. Accordingly, the lower and upper limits of the critical amount of corrosion were 8-25%, respectively.
Evaluation of the cementing efficiency factor of low-calcium fly ash for the chloride-penetration resistance of concretes: A simple approach
Huynh, PT; Ogawa, Y; Kawai, K; Bui, PT
CONSTRUCTION AND BUILDING MATERIALS, Vol.270, 2021, FEB 8.
(https://doi.org/10.1016/j.conbuildmat.2020.121858)
Abstract
This paper aims at simply evaluating the cementing efficiency factor (k-value) of low-calcium fly ash (FA) for the chloride-penetration resistance of concretes using the chloride-penetration depth (x(d)). Results indicate that x(d) could be used as a concrete-durability property to obtain the k-value of FA in a simple approach compared to the chloride-diffusion coefficient. The k-value of the FA based on the x(d) was approximately higher than 2, and it increased linearly with the increment in the FA reaction degree subsequent to the start of immersion. In addition, the correlation between the k-value for the chloride-penetration resistance and that for the strength development of the concrete was obtained.
Time-variant probabilistic assessment of corrosion initiation of marine concrete structures considering maximum phenomenon
Leng, Y; Lu, ZH; Li, CQ; Zhao, YG
CONSTRUCTION AND BUILDING MATERIALS, Vol.272, 2021, FEB 22.
(https://doi.org/10.1016/j.conbuildmat.2020.121967)
Abstract
This study presents a new dual time-variant chloride diffusion model considering maximum phenomenon for concrete structures exposed to marine environment. The model is developed from the assumption that the concentration gradient is the sole or dominant driving force for chloride ingress in concrete, and both the chloride diffusion coefficient and peak chloride content are considered as time-variant. The applicability and accuracy of the developed model are verified by comparing the fitted and predicted chloride profiles with field data. Based on the developed model, time-variant probabilistic evaluation of corrosion initiation in a typical prestressed box girder located near coast is carried out. Results reveal that the maximum phenomenon has a significant effect on the prediction of the time to corrosion initiation. The results of sensitivity analysis indicate that the critical chloride content is the decisive parameter in the prediction of the corrosion initiation time, followed by the relative humidity, water-to-binder ratio, temperature, thickness of concrete cover, etc. Besides, the effects of the correlation between random variables and the distance from the coast on the time-variant probability of corrosion initiation are investigated. It is found that the correlation among random variables should be considered, and the effect of distance from the coast on the time-variant probability of corrosion initiation is sharply decreasing at a very short distance from the coast.
SIBIE application to detecting void at post-installed adhesive anchor in concrete
Mumand, F; Nagai, Y; Shigeishi, M
CONSTRUCTION AND BUILDING MATERIALS, Vol.272, 2021, FEB 22.
(https://doi.org/10.1016/j.conbuildmat.2020.121916)
Abstract
Stack Imaging of spectral amplitude based on the Impact Echo so-called SIBIE is among the recent techniques of nondestructive inspection. The current study addresses its application to detect voids in anchor-bolts and its applicability for periodic inspection through the shift in the magnitudes of amplitudes. Anchor-bolts have extensive usage in concrete structures and their periodic inspection and maintenance are necessary. SIBIE post-analysis of Impact-echo data has been performed to detect the artificial voids in concrete specimens. The analyses were performed in three stages (intact, hole-drilled, and anchor-fixed) of the grout and epoxy-resin based fixed anchor fixations. Four methods (7.9 mm, 6.4 mm, and 4.6 mm steel balls' free drop, and spring impactor with titanium bullet) were used to generate elastic stress waves in concrete. The artificial voids of 4 cm and 5 cm depths were detected in grout and epoxy-resin based fixed anchors. The FFT analysis reveals the shift in the magnitude of amplitudes while SIBIE analysis provides a more comprehensive image of the scenario. The amplitudes' shift indicates apparent effects of hole-drilled, and anchor-fixed stages from the intact. It was indicated that the amplitude intensity of reflecting frequencies is higher before the hole-drilled stage, it has decreased when the hole of anchor fixation has been drilled and recovered back as the anchor has been fixed.
Microstructure-dependent corrosion and passivation of iron with a high carbon content in weak alkaline solution
Nikamoto, T; Sasaki, H
CONSTRUCTION AND BUILDING MATERIALS, Vol.269, 2021, FEB 1.
(https://doi.org/10.1016/j.conbuildmat.2020.121297)
Abstract
The corrosion of metallic Fe grains present in steelmaking slag used in road construction is a cause for concern. In this study, we examined the behaviors of Fe-3.8 wt%C and Fe-4.4 wt%C alloys in borate buffer solutions (pH 9) and compared them with those of two types of commercial steel bars for a better understanding of unrefined Fe corrosion in weak alkaline environments. The influences of the alloy microstructures and Cl ions were evaluated via open circuit potential measurements and linear sweep voltammetry. These measurements revealed that Fe with high C content exhibited greater corrosion resistance after quenching and was passivated in a solution containing Cl, which corroded the commercial steel bars and slow-cooled alloys tested. In a solution containing real steelmaking slag, the Fe-C alloys and commercial steel bars did not corrode for at least 3 months when decarburization slag was used due to its high basicity. The Fe-C alloys exhibited either passivation or corrosion when dephosphorization slag was used. Although the inhomogeneity of actual steelmaking slag affected the reproducibility of these tests, the quenched alloys showed higher tendency toward passivation compared with the commercial steel bars and slow-cooled alloys.
Effect of copper slag fine aggregate on corrosion processes and behavior in reinforced concrete prism specimen
Sandra, N; Kawaai, K; Ujike, I
CONSTRUCTION AND BUILDING MATERIALS, Vol.271, 2021, FEB 15.
(https://doi.org/10.1016/j.conbuildmat.2020.121909)
Abstract
This paper reports the result of experimental on the resistance to chloride diffusion and steel corrosion of concrete mixtures. A series of tests were performed to investigate the effect of copper slag as partial replacement of fine aggregate on corrosion processes and behavior in prism specimens. Chloride migration tests in steady-state were executed at the age of 28 and 91 days in accordance with Japan Society of Civil Engineers (JSCE) G571-2003 to determine the diffusion coefficient of chloride ions permeated through concrete specimens. In addition, some electrochemical tests were carried out through the repeated wet and dry (NaCl 10%) cycles up to 1 year to examines the probability of corrosion of steel bars in concrete, corrosion current density, and the rate of oxygen permeability. Based on the chloride migration test, which was obtained from the cumulative increase of chloride ion concentration, the results indicate that concrete with a longer curing period achieved lower chloride-ion concentration, thus suggesting that there is an increase in the resistance of concrete against chloride attack. The chloride penetration depth and distribution of chloride content in CUS prism specimens after exposure to wet and dry cycles for one year are almost similar to those of the OPC specimens. Thus, the durability performance of CUS concretes with respect to the resistance against chloride ingress was comparable to that of OPC concrete. Besides that, it is generally recognized that the incorporation of fly ash in blended cement by its the pozzolanic reaction of fly ash improves concrete protection against chloride-induced corrosion of steel bars by reducing its diffusivity and the rate of oxygen permeability.
Study on the correlation between the compressive strength of hardened cement paste and the physical properties of drilling powder
Tanaka, S; Sakai, Y
CONSTRUCTION AND BUILDING MATERIALS, Vol.269, 2021, FEB 1.
(https://doi.org/10.1016/j.conbuildmat.2020.121815)
Abstract
A fundamental study was conducted to develop a method for estimating the compressive strength of concrete with minimal damage. This study focused on the strength development of hardened cement to determine whether the strength of the cement paste could be estimated from the properties of the drilling powder. The helium true density, particle size distribution, and pore volume of drilling powder samples collected from the specimens were measured and compared with the compressive strengths of the specimens. It was determined that the information that governs the compressive strength of the hardened cement remained in the pore structure of the drilling powder.
Investigation of the carbonation performance of cement-based materials under high temperatures
Wang, DC; Noguchi, T; Nozaki, T; Higo, Y
CONSTRUCTION AND BUILDING MATERIALS, Vol.272, 2021, FEB 22.
(https://doi.org/10.1016/j.conbuildmat.2020.121634)
Abstract
The waste carbon dioxide generated in heavy industries usually accompanies by high temperatures and vapor. To fully utilize the high temperature and improve the carbon dioxide sequestration efficiency, this study has tested and evaluated the carbonation performance of cement paste in a broad temperature range from 20 degrees C to 300 degrees C. The results indicate that carbonation speed could be effectively improved under high temperatures in a short period (1 h) at the liquid water existing conditions. Besides, relative humidity and water to cement ratio effect at 100 degrees C were also investigated. The carbonation mechanisms at different vapor content have been explored from the viewpoint of carbonate substances transportation in high-temperature environments. The contribution of hydrated products to calcium carbonate varies with vapor content, and the high carbonation speed usually accompanies by the generation of the metastable calcium carbonate.
Simulation of steel fibre reinforced concrete using RBCS discrete model
Mehrpay, S; Ueda, T
CONSTRUCTION AND BUILDING MATERIALS, Vol.266, 2021, JAN 10.
(https://doi.org/10.1016/j.conbuildmat.2020.120889)
Abstract
As a complementary part of a previously developed discrete model, Rigid Body Coupled Spring (RBCS), the model is extended to simulate and predict the behaviour of Steel Fibre Reinforced Concrete (SFRC) by modifying mesoscopic shear material model and introducing fibre contribution to mesoscopic tensile material model with respect to the inclined fibre pull-out behaviour. Several types of rounded-straight steel fibre with various volume fractions were used in these simulations and the outcome was compared with related experimental studies. Studied cases include uniaxial compressive behaviour, direct tension behaviour, flexural and direct shear behaviour. The results have confirmed the success of this approach in the studied cases.
Experimental investigation of pozzolanic reaction and curing temperature-dependence of low-calcium fly ash in cement system and Ca-Si-Al element distribution of fly ash-blended cement paste
Wang, T; Ishida, T; Gu, R; Luan, Y
CONSTRUCTION AND BUILDING MATERIALS, Vol.267, 2021, JAN 18.
(https://doi.org/10.1016/j.conbuildmat.2020.121012)
Abstract
Supplementary cementitious materials (SCMs) significantly improve concrete performance. However, the application of SCMs remains limited by their heterogeneity and variability. This study investigated the pozzolanic reaction and curing temperature-dependence of low-calcium fly ash in cement systems over 2 years. The experimental results show that fly ashes have different reactivities and temperature dependencies even though they have similar material properties. A modified tangential method was developed for thermogravimetric analysis of the calcium hydroxide content and chemically bound water of fly ash-blended cement paste. The chemical composition of an aluminium-modified calcium silicate hydrate (C-(A)-S-H) gel of fly ash-blended cement paste was studied by scanning electron microscopy-energydispersive X-ray spectroscopy (SEM-EDS) with image analysis. The experimental results show that as the Ca/Si ratio decreased in fly ash-cement paste, the Al/Si ratio increased. The Al/Si distribution of fly ash-blended cement paste varies widely from 0.05 to 0.50 with no specific maximum. The typical Ca/Si and Al/Si ratios of C-(A)-S-H gel in fly ash cement paste are approximately 1.40 and 0.25.