CEMENT & CONCRETE COMPOSITES (Elsevier Ltd.)
Numerical simulation and experiment on the coupled effects of macro-cell corrosion and multi-ion equilibrium with pseudo structural concrete
Wang, Z., Maekawa, K., Takeda, H., Gong, F.
CEMENT & CONCRETE COMPOSITES, Vol.123, 2021, OCT.
(https://doi.org/10.1016/j.cemconcomp.2021.104181)
Abstract
Corrosion of reinforcing bars in structural concrete is a critical deterioration issue. Corrosion could attribute to the electro-chemical reactions which are closely related to the electrical field and chemical substances. Generally, two types of corrosion are classified including the micro-cell and macro-cell corrosion depending on whether the anodic and cathodic polarization take place at the same location or not. This paper presented a numerical evaluation of macro-cell corrosion of structural concrete with integrating the electrical field and multi-ion kinetics in electrolyte. Space-averaged simulation method was adopted which allowed the analytical domain to be structural members, structures or even structure clusters instead of specific concrete-reinforcement interface. Experimental validation was also conducted with pseudo concrete materials to verify the reliability of numerical simulation where satisfied correlation was found.
Numerical method for predicting flow and segregation behaviors of fresh concrete
Xu, Z., Li, Z.
CEMENT & CONCRETE COMPOSITES, Vol.123, 2021, OCT.
(https://doi.org/10.1016/j.cemconcomp.2021.104150)
Abstract
Current meshless particle methods are able to simulate the flow of fresh concrete, but fail to predict the segregation since fresh concrete is regarded as homogeneous fluid. This study aims to develop a numerical approach to predict the segregation of coarse aggregate (CA) in fresh concrete together with the flow behavior. A double-phase & multi-particle (DPMP) model was proposed to describe fresh concrete, which treats fresh concrete as a double-phase fluid composed of matrix mortar and the CA particles that had random shapes, size distribution, and different density from matrix mortar. Each CA particle was formed by the element particles, of which number was dependent on the size and shape of described CA particle. Three types of inter-particle interaction, including CA-CA particles, CA-mortar particles, and two mortar particles, were investigated, respectively. Then, based on the complete implicit MPS (I-MPS) method and the DPMP model, the L-box flow of two series of high fluidity concrete were simulated. The ability of the proposed numerical approach to simultaneously simulate the flow and segregation behaviors of fresh concrete was confirmed. Moreover, this numerical method can analyze the changes of localized rheological parameters of segregated concrete.
Development of alkali-silica reaction model considering the effect of aggregate size
Joo, H.E., Takahashi, Y.
CEMENT & CONCRETE COMPOSITES, Vol.122, 2021, SEP.
(https://doi.org/10.1016/j.cemconcomp.2021.104149)
Abstract
The expansion of concrete members due to the alkali-silica reaction (ASR) is influenced by various factors such as temperature, humidity, aggregate size, aggregate reactivity, and alkali components; among these factors, the aggregate size induces a pessimum effect in which maximum expansion due to the ASR appears in aggregates of a specific size. This makes it extremely difficult to define the relationship between aggregate size and the expansion of concrete in a simple manner. Therefore, this study aims to develop a model to estimate the expansion of concrete members subjected to ASR, taking the pessimum effect of fine aggregate (i.e., sand) size less than 5.0 mm into consideration. Based on a multi-scale chemo-hygral computational system developed by the authors in previous research, the alkali adsorption mechanism was introduced for a phenomenon in which the expansion reduces as the aggregate size decreases, while the mechanism of reduction in the penetration depth ratio of the ASR gel was introduced for a phenomenon in which the expansion reduces as the aggregate size increases. The proposed model was verified in detail by comparing it with ASR test results according to the aggregate size reported in the literature. It was found that the proposed model reasonably evaluated both the expansion of specimens according to the aggregate size and the pessimum effect that resulted in the maximum expansion of concrete members at a specific aggregate size.
Influence of bending cracks on the distribution of rebar corrosion in SHCC
Kobayashi, K., Hosokawa, K., Hattori, Y., Yun, H.-D.
CEMENT & CONCRETE COMPOSITES, Vol.122, 2021, SEP.
(https://doi.org/10.1016/j.cemconcomp.2021.104146)
Abstract
SHCC is a construction material that exhibits pseudo strain-hardening properties under tensile/bending stresses, and is expected to have high resistance against intrusion of aggressive agents because of its fine cracks. In this study, the chloride penetration resistance and rebar corrosion proof performance of SHCC compared to ordinary concrete were investigated over a test period of one year. Two types of bending cracks, one simulating a live load crack (LLC) and the other a dead load crack (DLC), were introduced into steel-reinforced SHCC/concrete beams to investigate the influence of bending cracks on the onset and progress of rebar corrosion in the beams. The corrosion area and corrosion loss of rebar in SHCC were significantly lower than in a concrete with the same water cement ratio. The rebar corrosion localized around cracks in SHCC with a water cement ratio of 0.3, but tended to be more dispersed when the water cement ratio was 0.4. In beams with the same amount of deformation, LLC caused more severe corrosion than DLC
Influences of moisture change and pore structure alteration on transport properties of concrete cover
Yokoyama, Y., Nakarai, K., Sakai, Y., Kishi, T.
CEMENT & CONCRETE COMPOSITES, Vol.122, 2021, SEP.
(https://doi.org/10.1016/j.cemconcomp.2021.104090)
Abstract
This study proposes a new method to analyze important factors that affect the air permeability of concrete cover. By conducting non-destructive tests on mockup box culvert specimens exposed to the outdoors (without rainfall), the changes in the moisture content, air permeability, and water absorption of concrete cover were investigated over a period of four years. Furthermore, the changes in their pore structure from 2.6 to 38 months were examined. The results clarified that the measured air permeability coefficient increased with age due to drying. Moreover, this study confirmed high correlation between the air permeability and total pore volume measured from the concrete after sufficient drying. Using the obtained equations, the influence of moisture change and pore-structure alteration on the air permeability coefficient were analyzed. This study reveals that their degree of influence is altered by the cement type and curing period.
The influence of restraint on the expansion of concrete due to delayed ettringite formation
Kawabata, Y., Ueda, N., Miura, T., Multon, S.
CEMENT & CONCRETE COMPOSITES, Vol.121, 2021, AUG.
(https://doi.org/10.1016/j.cemconcomp.2021.104062)
Abstract
The influence of restraint on expansion, expansive pressure, and cracking patterns due to delayed ettringite formation (DEF) in concrete was experimentally evaluated. Especially, the expansive pressure was estimated with two approaches: calculation from the strain of the steel and direct measurement using load cells. The expansive behaviors were strongly affected by the restraint, especially in the restraint direction. The expansive pressure measured by the load cell was 1.9?3.9 MPa, which is nearly consistent with those calculated from the steel bar strain. The expansive pressure of DEF was almost the same order of magnitude as for ASR expansion, despite larger free DEF expansion than ASR. From a simplified calculation, it is estimated that the imposed DEF expansion was reduced from the stress-free expansion by approximately 80%. Although the total length of surface cracking was independent of the degree of the restraint, the distribution of surface cracks was significantly modified by the degree of the restraint. On the contrary, the inner crack pattern was similar for the restraint case while large gap formation was observed for the stress-free case.
Electrostatic properties of C?S?H and C-A-S-H for predicting calcium and chloride adsorption
Yoshida, S., Elakneswaran, Y., Nawa, T.
CEMENT & CONCRETE COMPOSITES, Vol.121, 2021, AUG.
(https://doi.org/10.1016/j.cemconcomp.2021.104109)
Abstract
The adsorption capacity of cement hydrates considerably affects the ionic ingress into cementitious materials. In this study, the surface electrostatic properties of calcium silicate hydrate (C–S–H) and calcium aluminosilicate hydrate (C-A-S-H) were determined to understand the effects of the properties on calcium and chloride adsorption. The density of the surface functional groups was determined by analysing the structure of C–S–H and C-A-S-H through 27Al and 29Si MAS NMR. The surface sites of ≡SiOH and ≡AlOH are available in C-A-S-H whereas C–S–H has ≡SiOH groups for ionic adsorption. We found that the incorporation of aluminium decreases the number of total adsorption sites in C-A-S-H. Furthermore, the site density increased with Ca/(Si + Al). To understand the C-A-S-H/solution interface, a triple-layer surface complexation model was developed and the associated equilibrium constants for deprotonation, calcium, and chloride adsorption were determined by fitting the experimental data of potentiometric titration and zeta potential measurement results. The estimated surface complexation modelling parameters were verified by predicting the experimental data of calcium and chloride adsorption on C–S–H and C-A-S-H.
Bond behavior evaluation of deformed rebar dependent on lateral pressure confinement including various structural parameters
Farooq, U; Nakamura, H; Miura, T
CEMENT & CONCRETE COMPOSITES, Vol.119, 2021, MAY.
(https://doi.org/10.1016/j.cemconcomp.2021.103996)
Abstract
An analytical method based on Three-Dimensional Rigid Body Spring Model (3D RBSM) was proposed to evaluate the bond behavior of deformed rebar in RC structures dependent on lateral pressure confinement conditions. The method used voronoi mesh and beam element to model concrete and reinforcement respectively that was previously proposed by authors to simulate split failure only. In this study, applicability was extended to evaluate transition from split to pullout failure by extending proposed local bond model. It was confirmed that this simple beam element-based model can reproduce experimentally observed bond behavior dependent on various lateral pressure levels and frictional conditions. Most importantly, method can evaluate the internal cracking and stress distribution governed failure mechanisms dependent on confinement conditions. Meanwhile, in comparison to FEM and RBSM based models with 3D formation of rebar with rib, the proposed model is an efficient and economical alternative to evaluate confinement effects in RC members.
Mesoscale simulation of pull-out performance for corroded reinforcement with stirrup confinement in concrete by 3D RBSM
Avadh, K; Jiradilok, P; Bolander, JE; Nagai, K
CEMENT & CONCRETE COMPOSITES, Vol.116, 2021, FEB.
(https://doi.org/10.1016/j.cemconcomp.2020.103895)
Abstract
The confining effect of concrete cover and stirrups reduces the rate of bond deterioration due to corrosion. However, the large dispersion in recorded experimental data makes it difficult to clearly separate the influence of cover depth and stirrup confinement on bond degradation. This study utilises the discrete 3D Rigid Body Spring Model (RBSM) to conduct a meso-scale investigation regarding the effect of cover thickness and stirrup confinement on internal crack evolution and pull-out behaviour in corroded reinforced concrete models. The simulation scheme is divided into two stages. In stage 1, different degrees of corrosion are introduced, producing cracking in the cover concrete; in stage 2, the corroded main reinforcement is pulled out from the damaged concrete. 3D RBSM is advantageous because the concrete is randomly meshed to reduce mesh bias on crack propagation and the actual geometry of the deformed bars is modelled. The simulation results clarify that the presence of thicker cover delays crack initiation but increases the rate of crack opening. Stirrups do not have any significant effect on crack initiation but effectively restrict crack growth. An investigation of the internal stress in the simulation models shows that tensile stresses generated in stirrups during corrosion are responsible for reactionary confining pressure that restricts crack propagation. Load-displacement curves show reductions in pull-out capacity, stiffness and ductility with increasing corrosion damage. The relative influence of crack opening and stirrup volume on the rate of bond degradation with respect to average surface crack width are discussed and compared with published experimental results and an empirical equation.