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Hardened concrete is a three-phase composite consisting of cement paste, aggregate and interface between cement paste and
aggregate. The interface in concrete plays a key role on the overall performance of concrete. The interface properties such
as deformation, strength, fracture energy, stress intensity and its influence on stiffness and ductility...
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Citations
... The ITZ has been considered as the weak zone owing to higher porosity (Diamond and Huang 2001;Scrivener et al. 2004), lower strength (Monteiro and Andrade 1987;Zimbelmann 1985), fracture energy (Rao and Prasad 2011), and Young's modulus (Jebli et al. 2018;Xie et al. 2015) compared to the bulk cement or mortar. Therefore, the constitutive models of ITZ developed by (Sasano and Maruyama 2021) were introduced for normal and shear springs at the interface between mortar and aggregate as shown in Fig. A2. ...
Moisture transport is the key phenomenon indicating the deterioration of the durability and structural performance of concrete structures. Although various studies have attempted to evaluate moisture transport in concrete, an anomalous behavior, which does not follow the root-t law compared to other porous material, was not explicitly taken into account. To quantitatively evaluate anomalous moisture transport, this study developed a couple of numerical methods between the truss-network model (TNM) and the rigid-body-spring model (RBSM) for this purpose. The colloidal behavior of calcium-silicate-hydrate (C-S-H), which is the major phase of cement-based material, was introduced to consider the anomalous behavior and mechanical response regarding the microstructural change of cement paste as well as cracks that significantly accelerate the moisture transport in concrete. The numerical results indicated that both microstructural change of cement paste and rapid absorption through cracks cause anomalous behavior. In addition, the numerical results suggest that volumetric change of cement paste should rely on water content related to the colloidal behavior of C-S-H in order to reproduce the realistic expansion and the closure of cracks during a rewetting process that affects structural performance and durability of concrete.
... For the concrete, surface (micro)roughness of coarse aggregates influences the cement suspension viscosity [2,3,31] and the interfacial bonding strength of concrete [23,24,3,46,47], but its characterization method is not consolidated and still a research challenge. The most traditional method for evaluating roughness [10,51], the mechanical profiling, is still a widely used one due to its simplicity; however, it may cause micro and nanoscale damage on the samples ( [14,26,49]). ...
Surface (microscale) roughness of coarse aggregates influence the cement suspension' viscosity and the inter-facial bonding strength of concrete, but its characterization method is not consolidated and still a research challenge. 3D scanner determines accurately the shape, volume, but it is incapable of describing the roughness at microscale. Roughness at microscale (surface index-cm 2 /cm 2) can be measured accurately using interferom-etry, but it cannot describe shape and volume of the particles. Once the volume of aggregate particles may vary 200% and it seems crucial to establish the (micro)roughness per volume (cm 2 /cm 3) to better understand the effects in the properties of cementitious materials. This paper presents a method of obtaining volumetric surface area of coarse aggregates at micrometric scale by joining (cm 2 /cm 3) both techniques. Three types of aggregates were assessed: gneiss, low-grade meta-carbonate (dolomite) and quartzite (gravel), with one hundred particles in the size range of 4.75 mm to 37.5 mm. For coarse aggregates, the larger the particles, the more of their surface area will be influenced by (mesoscale) shape and less by surface (microscale) roughness. However, the smaller the particles, SI index will differ considerably. The surface area determined by the method proposed in this paper provides a good correlation with the methylene blue method.
... where E 0 is the initial elastic stiffness of the cement-based matrix; ε pl c refers to the compressive equivalent plastic strain; ε c is the total strain; d c represents the scalar initial stiffness damage variable. The corresponding yielding function proposed by Lubliner et al. [31] and modified by Lee and Fenves [30] is adopted and expressed as follows: ...
This paper investigates the interphase effect on the macro nonlinear mechanical behavior of cement-based solidified sand mixture (CBSSM) using a finite element numerical simulation method. CBSSM is a multiphase composite whose main components are soil, cement, sand and water, often found in soft soil foundation reinforcement. The emergence of this composite material can reduce the cost of soft soil foundation reinforcement and weaken silt pollution. Simplifying the CBSSM into a three-phase structure can efficiently excavate the interphase effects, that is, the sand phase with higher strength, the cement-based solidified soil phase (CBSS) with moderate strength, and the interphase with weaker strength. The interphase between aggregate and CBSS in the mixture exhibits the weak properties due to high porosity but gets little attention. In order to clarify the mechanical relationship between interphase and CBSSM, a bilinear Cohesive Model (CM) was selected for the interphase, which can phenomenologically model damage behaviors such as damage nucleation, initiation and propagation. Firstly, carry out the unconfined compression experiments on the CBSSM with different artificial gradations and then gain the nonlinear stress–strain curves. Secondly, take the Monte Carlo method to establish the numerical models of CBSSM with different gradations, which can generate geometric models containing randomly distributed and non-overlapping sand aggregates in Python by code. Then, import the CBSSM geometric models into the finite element platform Abaqus and implement the same boundary conditions as the test. Fit experimental nonlinear stress–strain curves and verify the reliability of numerical models. Finally, analyze the interphase damage effect on the macroscopic mechanical properties of CBSSM by the most reliable numerical model. The results show that there is an obviously interphase effect on CBSSM mechanical behavior, and the interphase with greater strength and stiffness ensures the macro load capacity and service life of the CBSSM; a growth in the interphase number can also adversely affect the durability of CBSSM, which provides a favorable reference for the engineering practice.
... Dry silica is stored in silos and hoppers, while wet products are stored in tanks. The chemical composition of silica fume is given in Table 3 [65][66][67][68][69][70]. Silica fume consists of very fine vitreous particles with a surface area on the order of 20,000 m 2 /kg, which is approximately 100 times smaller than the average cement particle. ...
Supplementary cementitious materials (SCMs) and chemical additives (CA) are incorporated to modify the properties of concrete. In this paper, SCMs such as fly ash (FA), ground granulated blast furnace slag (GGBS), silica fume (SF), rice husk ash (RHA), sugarcane bagasse ash (SBA), and tire-derived fuel ash (TDFA) admixed concretes are reviewed. FA (25–30%), GGBS (50–55%), RHA (15–20%), and SBA (15%) are safely used to replace Portland cement. FA requires activation, while GGBS has undergone in situ activation, with other alkalis present in it. The reactive silica in RHA and SBA readily reacts with free Ca(OH)2 in cement matrix, which produces the secondary C-S-H gel and gives strength to the concrete. SF addition involves both physical contribution and chemical action in concrete. TDFA contains 25–30% SiO2 and 30–35% CaO, and is considered a suitable secondary pozzolanic material. In this review, special emphasis is given to the various chemical additives and their role in protecting rebar from corrosion. Specialized concrete for novel applications, namely self-curing, self-healing, superhydrophobic, electromagnetic (EM) wave shielding and self-temperature adjusting concretes, are also discussed.
... These interfaces experienced higher shear stresses because of the flexural loading. However, because the mesoscale strength in Mode II usually is several times higher than that in Mode I (Rao and Prasad 2011), these interfaces are less prone to fracture. The net effect of this was slower flexural crack growth in the 8A specimen than in the 8R specimen. ...
A recently developed discrete-element capability was used to study the effect of mesogeometry on flexural failure in concrete. Fabric anisotropy in angular specimens was found to retard flexural crack growth. The fabric also played a key role in determining
the geometry of the fracture process zone. Greater dispersion in the local fabric resulted in more tortuous cracks. Specimens with angular particles exhibited more crack branching and tortuosity, and hence had higher macrofracture energy, than specimens with rounded aggregates. Aggregate shape affected the peak stress and postpeak response of notched specimens. The slowing of crack growth and nonmonotonic
evolution of the fracture process zone, also observed in experiments, was investigated. Crack tip shielding was found to play a critical role in explaining this behavior.
... There is some consensus in the literature that increasing the roughness of aggregate particles increases the bond strength in the transition zone between cement paste (generally fluid) and aggregate, causing an increase in concrete strength in the hardened state [1][2][3][4][5]. The aggregate irregularities are not the only factor affecting the strength of concrete; the strength of aggregate can also limit the strength of concrete. ...
Surface roughness of coarse aggregates, regardless of its known influence in the bonding strength with the cement paste in the hardened state and in the viscosity of the composite in the fresh state, it still a barely researched and discussed topic. In addition, little is known about what rock characteristics influences the multiscale roughness of aggregates. This paper aims to evaluate the roughness of distinct types of aggregates in multiscale (macro and micro scale of roughness) using a 3D interferometer and establish a quantitative relation between the granulometry and mineral composition of the rocks and the surface roughness of aggregates. Six types of aggregates, five crushed and one gravel from riverbed, with sizes ranging from 19 to 25 mm were scanned. One sample from each type was chosen for a petrographic analysis. The six types of aggregates analyzed showed statistical differences between them in macro and micro scales of roughness. In the microscale roughness, basalt was considered the smoothest, and surprisingly, the quartzite (gravel), were one of the roughest. In the macro scale roughness, the quartzite (the gravel) was smoother than all the other samples due its rounded shape, while the gneiss was the most irregular particle and had the highest roughness. The quartzite (gravel) is a good example of how an aggregate could be very rough in a microscale (invisible to the naked eye), comparable to crushed aggregates, while being smooth to the touch and rounded. The weathering seems to affect the roughness at micro(nano)scales, independently of the roundness shape observed at millimetric scale. The micro scale roughness appeared to be related to the average size of the grains, the smaller the average grain size, the lower the micro scale roughness is. Rocks with aphanitic textures tends to fracture in smoother surfaces than rocks with phaneritic textures.
... It is generally accepted that the ITZ-the interface between cement paste and aggregate-has higher porosity [46,47] and lower strength (and hardness) [48][49][50][51], fracture energy [52], and Young's modulus [53,54] than bulk cement paste or mortar. Furthermore, some studies have found that the impact of the ITZ properties on the concrete properties cannot be neglected. ...
Although many studies have found that drying alters the mechanical properties of concrete, the mechanism behind this change remains unclarified. The aim of this study is to elucidate the mechanism of change in properties of concrete after drying through the numerical calculation: a 3D mesoscale rigid-body-spring model (RBSM) with three phases, i.e. mortar, aggregate, and the interfacial transition zone while considering the properties changes of mortar due to drying. Based on the RBSM results, it is concluded that the change in compressive strength due to drying and heating is determined by a balance of the impact of drying-induced microcracking around coarse aggregates and the change in mechanical properties of the mortar due to drying. These mechanisms change the applied load required to reach the critical crack width and distribution, at which rim of the specimen begins to isolate from the core region and the load sustained by the rim decreases.
... Also worth investigating are issues such as how confining pressure affects microcrack growth, mesolevel slip, shear banding, and localization. The nature of cracking in confined concrete is also of interest; it is well known that crack growth in normal-strength unconfined concrete largely occurs along the aggregate mortar interface (Neville 1995), whereas in high-strength concrete, there is increased cracking in the mortar (Calixto 2002). Does the mobilization of passive confinement, and consequent increase in concrete strength [cf. ...
The paper attempts to understand the macroresponse of fiber-reinforced polymer (FRP) confined concrete in terms of mesolevel interactions. Cylindrical specimens are modeled using a three-dimensional (3D) discrete-element formulation that uses polyhedrons of required geometry to closely approximate the actual shape and size of coarse aggregates. A coupled discrete-continuum approach is adopted to account for damage at length scales smaller than the smallest particle modeled. Constitutive models that capture aspects of mesobehavior crucial to confined concrete are developed, and mesoscale features affecting interface cracking, slip, and mortar damage are investigated. Increased confinement is seen to lead to some reduction in Mode I cracking and a marginal increase in Mode II cracking at the interfaces. However, the principal mechanism for strength gain is seen to be the prevention of localization and dispersal of slip. Increase in confining stiffness also results in increased mortar damage, which limits strength gain due to confinement, as well as a remarkable reversal of the platen effect.
... (a) Choice of damage initiation stress: Experimental data on interfacial fracture properties of concrete is limited. Recently, Rao and Prasad [45] performed experiments to determine damage parameters for mortar-rock interfaces. The damage initiation stress values reported in this paper are used as the mean values of the respective Weibull distributions. ...
A three-dimensional discrete element modelling capability for concrete based on rigid particles of arbitrary shape and size has been developed. The novel particle generation algorithm allows control of particle size, angularity and flakiness. General rigid body kinematics including finite rotations is accounted for, and an explicit time integration algorithm that conserves energy and momentum is implemented. An efficient contact algorithm with several features to increase the efficiency of the contact computations has been developed. This enables the gravity packing problem for arbitrary shaped particles to be solved in reasonable run time. The proposed procedure is used to generate assemblies of concrete specimens of various sizes that are homogeneous and isotropic in the bulk, and can capture the wall effect due to the formwork. The calibrated specimens are seen to be capable of accurately capturing experimentally observed macro stress strain response and failure patterns. The influence of aggregate shape on texture formation in the packed specimen, and on macro strength and failure patterns in hardened concrete, is demonstrated and is seen to be consistent with experimental results.
... The dark regions correspond to interfaces between aggregates and cement matrix, eroded due to water flow. The strength of the cement matrix as well as that of the cement/aggregate-interface in composite 1 is rather low because of the high water-cement ratio [14,15]. These low-strength regions are preferred locations for water flow erosion [16][17][18]. ...
The objective of the paper is the quantification of effects of erodent flow kinetic energy and exposure time on the erosion of cement-based composites with high-speed hydro-abrasive jets. The erodent flow kinetic energy is varied due to changes in erodent velocity, traverse rate and erodent particle mass-flow rate. For a given traverse rate, the relationship between volumetric erosion rate and erodent flow kinetic energy follows a power function with power exponents between 0.49 and 0.66. The kinetic energy of the erodent flow is not a sufficient measure for the material removal capacity of high-speed hydro-abrasive flow. A critical exposure time must be realized in order to eliminate traverse rate effects. Exposure time effects are characterized with a Weibull-type function, whereby the shape parameter k of the function depends on erosion mode and material response. If incremental erosion modes dominate the material removal process: k>1. If continuous erosion modes control the material removal process: k≤1. It is supposed that k exceeds unity if a threshold fracture toughness of the composites is exceeded.
