Effect Of Coarse Aggregate Research Articles

Mechanical and autogenous shrinkage properties of coarse aggregate ultra-high performance concrete (CA-UHPC): The effect of mineral admixtures

To reduce the shrinkage and explore the best content of mineral admixtures of coarse aggregate ultra-high performance concrete (CA-UHPC), this study conducted 12 groups of autogenous shrinkage, basic material properties (compressive strength, tensile strength, and flowability), and X-ray diffraction experiments on CA-UHPC with coarse aggregate and different amounts of mineral admixtures (slag powder, limestone powder). The effects of coarse aggregate and mineral admixtures on the autogenous shrinkage and basic material properties of CA-UHPC were analyzed, and the measured values of CA-UHPC autogenous shrinkage strain were compared with the theoretical values calculated by six commonly used concrete shrinkage prediction models. The experimental results show that under the condition of 15 % coarse aggregate content and no steam curing, a CA-UHPC with a compressive strength greater than 110 MPa, a tensile strength greater than 11 MPa, a flowability greater than 290 mm, and an autogenous shrinkage of less than 700 after 120d can be obtained. The mineral admixture has a significant impact on the fundamental properties of CA-UHPC. The compressive strength, tensile strength, and flowability of CA-UHPC with 15 % limestone powder and 15 % S95 slag powder increased by 6.6 %, 5.4 %, and 27.6 % compared to UHPC with only coarse aggregate added, and the autogenous shrinkage after 120 days decreased by 10.5 %. However, when the dosage of limestone powder and S95 slag powder exceeds 30 %, the tensile and compressive strength of CA-UHPC will rapidly decrease. This study also revised the GL 2000 shrinkage prediction model based on the CA-UHPC autogenous shrinkage test results, introduced the influence coefficient of mineral admixture content on autogenous shrinkage strain, and established a theoretical calculation model suitable for CA-UHPC autogenous shrinkage strain.

Effects of coarse aggregates on 3D printability and mechanical properties of ultra high performance fiber reinforced concrete

3D printing of ultra high performance fiber reinforced concrete (UHPFRC) suffers from high shrinkage and poor interlayer properties. To mitigate these problems, this study develops new mixtures of UHPFRC materials containing coarse aggregates (CA), and critically examines their suitability for 3D printing (3DP). Totally 90 mould-cast and 3DP cylinder and beam specimens with different CA sizes (5–15 mm) and CA-binder ratios (0.3–0.5) were tested under compression and bending in three directions. The internal distribution and volume fractions of steel fibers and pores and the crack trajectories were characterized and analysed by micro X-ray CT scanned 3D images with 37 μm voxel resolution. The results show that adding more and bigger CAs into UHPFRC reduced the flowability but enhanced the buildability with desired extrudability achieved by adjusting 3D printing velocity. Although the compressive strength of the 3DP cylinders was 15–42 % lower than that of the mould-cast ones due to higher porosities, over 100 MPa strength was still achieved for all the 3DP cylinders with less than 10 % anisotropy. The CT images did not show evident interlayers and interlayer delamination under compression, indicating the new 3DP mixtures and printing parameters may have highly promoted cement hydration. The flexural strength of 3DP beams was 3–34 % higher than that of the cast ones, because most fibres were oriented in the printing or beam axis direction as represented by overall orientation indices calculated from CT images, thereby providing significant crack-bridging effects. The developed new mixtures are therefore well suited for 3D printing, particularly for fabrication of structural members with preferred fibre orientation, such as beams, slabs and shells.

Effect of Coarse Aggregate and Multi-Wall Carbon Nanotubes on Heat Generation of Concrete

Many researchers are developing heating construction materials to remove black ice from roads, addressing the scientific challenges associated with this issue. The use of carbon-based nanomaterials in concrete is of great interest due to the excellent electrical and thermal conductivity of this material. In this study, the incorporation of multi-walled carbon nanotubes (MWCNTs) into concrete compositions results in the formation of MWCNT bridge networks. MWCNTs exhibit a low specific heat and possess the ability to promptly generate raised temperatures with minimal power input. This characteristic has the potential to induce temperature variations in concrete. The heat generation test parameters for MWCNT concrete included the mixing concentration of the MWCNTs, the mixing ratio of coarse aggregate, the water/cement (W/C) ratio, and the presence or absence of superplasticizers. The heating performance of concrete was found to improve as the mixing concentration of the MWCNTs increased, while a heating performance decrease was observed as the mixing ratio of coarse aggregate increased, owing to the reduced dispersibility of the MWCNTs. Conversely, the heating performance improved when the W/C ratio increased due to the enhanced dispersibility of the MWCNTs. Moreover, superplasticizers assist in dispersing MWCNTs, thereby improving the heating performance. Additionally, field emission scanning electron microscopy revealed that MWCNTs form a bridge network between the cement hydrates. As a result of this study, the maximum temperature variation of concrete mixed with MWCNTs was up to 73.6 °C. Therefore, by mixing MWCNT aqueous solutions with concrete and using an appropriate W/C ratio and superplasticizer, a new construction material capable of enhanced heating performance was developed.

Fibre alignment in fresh concrete with coarse aggregates and its visualization in transparent model concrete

Steel fibres distributed in concrete can greatly improve the mechanical performance of concrete, especially flexural and tensile behavior, if their orientations align to the direction of principal tensile stress. The study attempts to find diversified characters of fibre alignment in fresh concrete with consideration of adding coarse aggregates. A transparent concrete model, consisting of Carbopol gel, glass beads and crystals, is designed for the observation of fibre orientation. It shows good transparency and visibility, and can consider the effect of coarse aggregates since the volume fraction and particle size distribution of crystals are the same as coarse aggregates in real concrete mixture. The rheological properties of the model can be adjusted by the dosage of Carbopol and glass beads. Using this concrete model, the distribution and orientation of fibres can be directly observed and analyzed, considering the effect of aggregate sizes, concrete rheology and vibration time. The results show that coarse aggregates could limit the distribution space of fibres and lead to the decrease of fibre orientation coefficient. Fibre dispersion coefficient also decreases with the increase of aggregate sizes.

Effect of coarse aggregate and carbon fiber content on ohmic heating curing of concrete slab in realistic severely cold weather

In this work, carbon fiber-reinforced high-performance concrete (CF-HPC) slabs with coarse aggregate content of 25 vol%/35 vol%/45 vol% and carbon fiber content of 0.6 vol%/0.8 vol%/1.0 vol% were cured by ohmic heating (OH) curing under realistic severely cold condition for practical on-site construction. Results indicated that the coarse aggregate content has a substantial influence on the electrical resistance and curing time of concrete slab. Higher and lower content of coarse aggregate will lead to insufficient ohmic heats and curing time. On the contrary, carbon fiber content only has a limited influence on OH curing feature, such as slight value difference of electrical resistance and curing temperature. Besides, the correlation between the curing temperature of concrete slab and the associated factors (OH curing power, ambient temperature) was quantitatively analyzed. It is found that the OH curing power had a strong correlation with the concrete temperature during the most time of curing period, while the snowfall weather enhanced the correlation between ambient temperature and concrete temperature. At last, a criterion of feasible resistance range based on the experimental results and theorical analysis was proposed to evaluate the feasibility of OH curing and assist the concrete mix design.

The effect of coarse aggregate on the bleeding and mechanical properties of cemented paste backfill

The effect of coarse aggregate on the bleeding and mechanical properties of cemented paste backfill

Effects of coarse aggregates on the mechanical properties, durability and microscopic behaviour of mortar rubble

A new type of slope protection structure, mortar rubble arch slope protection, has good low-temperature performance, and it is mostly used in the seasonally frozen area of North China. To determine the effects of aggregate type (basalt, granite, limestone) and amount of coarse aggregate on mortar rubble, mechanical properties were measured and durability experiments were conducted. Compressive strength, bending strength, mechanical damage characteristics of the materials, freeze–thaw loss rates and temperature shrinkage coefficients were recorded. The results were verified by microscopic observations. Using the digital image correlation (DIC) test system, the main form of the bending failure of the mortar rubble was observed to be failure around the aggregate. Acoustic emission parameters were used to accurately reflect the damage characteristics of the mortar rubble during the compression test. The resistance time of basalt before failure was long, and its peak energy was high. The durability test results showed that granite mortar rubble had better frost resistance, a higher freeze–thaw resistance factor, and less temperature shrinkage deformation than the basalt and limestone rubbles, and it is more suitable for slope protection in cold areas. Scanning electron microscopy (SEM) results showed that the matrix entered the pores to form new bonds, which was the main reason for the high strength of the basalt specimens. The basalt mortar rubble interface was severely damaged after freezing and thawing. The optimal amount of added aggregate was approximately 60%-70%, which resulted in good mechanical properties and durability of the mortar rubble. When the flake aggregate content exceeded 70%, the strength and durability of the material decreased.

Effects of coarse aggregate and wavy steel fiber volumes on the critical stress intensity factors of modes I and III cracks in self-compacting concrete using ENDB specimens

This study investigated the effects of coarse aggregate and wavy steel fiber volumes on pure modes I and III fracture toughness (KIF & KIIIF) for which 72 Edge Notched Disc Bend (ENDB) specimens were made using four different coarse aggregate volumes (30, 40, 50 and 60%) and three different wavy steel fiber volumes (0.15, 0.3 and 0.45%). They were then examined with the three-point bending test. Results showed that increasing the coarse aggregate volume from 30% to 50% increased pure modes I and III fracture toughness, and increasing it from 50% to 60% reduced the fracture toughness because the fiber-coarse aggregate interaction caused fibers to negatively affect the resistance against fracture. The KIF-KIIIF comparison showed that the fiber effect was more evident and critical in the tearing mode (mode III). Since the fracture theory prediction criteria showed that the KIIIF/KIF ratio had a 0.7–0.9 variation range based on varying coarse aggregate and fiber volumes, it can be concluded that these criteria can well predict pure failure modes I and III of self-compacting concrete. Analysis of variance (ANOVA) was conducted on fiber-reinforced self-compacting concrete composites, and the post hoc Tukey test was used to study if the effects of the pairwise variables were significant on pure modes I and III fracture toughness.

Effect of Interface Transition Zone and Coarse Aggregate on Microscopic Diffusion Behavior of Chloride Ion.

Concrete is a multiphase composite material composed of coarse aggregate, cement mortar, and interface transition zone (ITZ). It is of great significance to study the effect of ITZ and coarse aggregate on chloride microscopic diffusion behavior for predicting the service life of reinforced concrete (RC) structures. By introducing the random distribution function, a random coarse aggregate model considering the randomness of the thickness of the ITZ was established. Furthermore, a two-dimensional (2D) chloride ion diffusion mesoscopic model was developed by specifying different diffusion properties for different phase materials of concrete. Moreover, the effects of coarse aggregate rate, ITZ thickness, and ITZ diffusion property on chloride ion diffusion behavior were investigated in this paper. The research showed that the aggregate has hindrance and agglomeration action on chloride ion diffusion. Although the volume content of the ITZ was very small, less than 0.2% of the total volume of concrete, the effect of the ITZ on the chloride diffusion in concrete cannot be ignored. More importantly, the mechanism of promoting chloride diffusion in the ITZ was revealed through the chloride diffusion trajectory. The research revealed the transmission mechanism of chloride ions in the meso-structure of concrete and provides theoretical support for the design of RC structures in coastal areas.

Numerical insights into the effect of ITZ and aggregate strength on concrete properties

Mechanical properties of concrete are highly dependent on its components. Consequently, a comprehensive understanding of the effects of aggregate and interfacial transition zone on concrete properties is important to applications. In this paper, a mesoscale investigation on the effects of coarse aggregate and interfacial transition zone strength on mechanical and fracture behaviours of concrete is investigated using discrete element modelling. The results show that the elastic modulus of concrete is insensitive to the strength of ITZ and aggregate, whereas the compressive strength and strain-to-damage highly depend on these two factors. An increase in ITZ/aggregate strength leads to a decrease of cracks in ITZ/aggregates and little change of cracks in mortar. Aggregate size, under certain conditions, can alter the crack growth process and result in distinct crack patterns.

The Effect of Aggregate Types on the Properties of Concrete

Concrete is an extensively used construction material due to its versatility, strength, durability, and ease in making various forms and shapes. The use of substandard materials, deficient quality concrete has been identified in the literature as the leading cause of building collapse in Nigeria. Aggregates strongly affect the concrete’s fresh and hardened properties, mixture proportions, and economy. More than 1 / 3 of the volume of concrete is occupied by the coarse aggregate, and any changes in rough aggregate type could affect its strength and fracture properties. This study examined the impact of coarse aggregates on the mechanical properties of concrete. Selected aggregates which are granite (igneous rock), schist (metamorphic rock), and sandstone (sedimentary rock), were used in this study. Aggregate Impact value and water absorption test were carried out for each of the aggregates used. A slump test was conducted on the fresh mixture for granite, schist, and coarse sandstone aggregates with river sand (fine aggregate) using a water-cement ratio of 0.50; it was observed that granite has a slump value of 35 mm, schist 28 mm, and sandstone 25 mm. Nominal mix (1:2:4) was adopted, and mix compositions were calculated using the absolute volume method. Twelve cubes (100x100 mm) and twelve cylinders (100x300 mm) were cast for each type of coarse aggregate. The specimens were cured by submersion. Three of the models were tested for 7, 14, 21, and 28 days to determine their compressive and splitting tensile strengths. Granite was found to have the highest average compressive strength of 16.00 N/mm 2 with an average density of 2575 kg/m 3 , compressive strength of schist was 15.17N/mm 2 with an average density of 2520 kg/m 3, while sandstone has the lowest average compressive strength of 12.33 N/mm 2 with an average density of 2500 kg/m 3 . Granite was found to have the highest moderate splitting tensile strength of 1.31 N/mm 2 with an average density of 4266.67 kg/m 3 , breaking tensile strength of schist was 0.99 N/mm 2 with an average density of 4256.67 kg/m 3 . In contrast, sandstone has the lowest average split tensile strength of 0.67 N/mm 2 with an average density of 4241.67 kg/m 3 . Densities and stability of the individual aggregates accounted for the variation in the concrete forces because of differences in properties and strength. In conclusion, the effect of coarse aggregate on the properties of concrete was identified, which will inform site concrete production of the suitability of aggregate selection in concrete work.

A modified numerical model for predicting carbonation depth of concrete with stress damage

A modified carbonation model centered on humidity-temperature-CO2 coupling was proposed. Its parameters were determined based on a 3-year natural carbonation test. The model was then verified by comparing carbonation results with that of accelerated experiment (2% and 20% CO2) and other publications. The effect of coarse aggregate, crack, and carbonation direction was investigated for undamaged concrete. The influence of stress damage (calculated by ABAQUS) and evaluating method was investigated for stress damaged concrete. The results indicated that the proposed model put more weight on the stress damage. It predicted the service life decreases to 1/3 of undamaged concrete for the example in this article.

Effect of medium coarse aggregate on fracture properties of ultra high strength concrete

Ultra high strength concrete (UHSC) originally proposed by Richards and Cheyrezy (1995) composed of cement, silica fume, quartz sand, quartz powder, steel fibers, superplasticizer etc. Later, other ingredients such as fly ash, GGBS, metakaoline, copper slag, fine aggregate of different sizes have been added to original UHSC. In the present investigation, the combined effect of coarse aggregate (6mm – 10mm) and steel fibers (0.50%, 1.0% and 1.5%) has been studied on UHSC mixes to evaluate mechanical and fracture properties. Compressive strength, split tensile strength and modulus of elasticity were determined for the three UHSC mixes. Size dependent fracture energy was evaluated by using RILEM work of fracture and size independent fracture energy was evaluated by using (i) RILEM work of fracture with tail correction to load – deflection plot (ii) boundary effect method. The constitutive relationship between the residual stress carrying capacity (σ) and the corresponding crack opening (w) has been constructed in an inverse manner based on the concept of a non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams. It was found that (i) the size independent fracture energy obtained by using above two approaches yielded similar value and (ii) tensile stress increases with the increase of % of fibers. These two fracture properties will be very much useful for the analysis of cracked concrete structural components.

Experimental Studies on Blast-Resistance of HFR-LWC Beams Enhanced with Membrane Action

Support-induced membrane action can enhance the resistance, while altering the failure pattern, of reinforced concrete (RC) members under static/dynamic loadings. Nevertheless, the membrane effect on the load-response is regarded as a safety factor in current design guides, hence, a thorough understanding of the resistance capability of RC members in the presence of membrane actions is considered essential. To quantitatively depict the membrane behavior and its influence on the blast-resistance and failure pattern of Hybrid Fiber Reinforced-Lightweight Aggregate Concrete (HFR-LWC) beams, a specially built end-constraint clamp is developed to provide membrane actions on the structural component subjected to the blast load simultaneously. A series of field tests are conducted to investigate the dynamic behaviors of the HFR-LWC beams under close-range detonations. Overpressure-time histories of shock waves induced by the close-range explosive charge are captured. Then the deflection-responses and failure modes of the HFR-LWC beams are further investigated. The responses of the clamped HFR-LWC beam under blast loadings can be well simulated, and the blast-resistances of the beam-type members with membrane action are evaluated reasonably. The results show that membrane action is beneficial for the bridging effects of hybrid fibers and the interlocking effects of coarse aggregate, thereby giving rise to the ductile failures of HFR-LWC beam. The maximum deflections of the clamped HFR-LWC beam decrease by about 60% compared with simply-supported HFR-LWC beam in this paper, illustrating that the blast-resistance may be seriously underestimated if the membrane effects are ignored in structural design.

2D Crack Propagation in High-Strength Concrete Using Multiscale Modeling

In this work a concurrent multiscale (macro and mesoscale) approach for high-strength concrete (HSC) is proposed for seeking to better understand the influence of coarse aggregate type, shape, and size distribution as well as the interfacial transition zone (ITZ) effects on the fracture mechanical responses. A linear elastic model with homogenized elastic properties is used for the macroscale, while a three-phase material composed of coarse aggregates, mortar matrix and the ITZ equipped with nonlinear behavior models are assumed for the mesoscopic level. To geometrically represent and gain insights into effects of coarse aggregates, two polygonal shapes are assumed: irregular quadrilateral and regular octagonal forms, which are used separated and randomly generated from a given grading curve and placed in the mesoscale region using the “take-and-place” method. A mesh fragmentation technique is used to explicitly represent the crack propagation process by considering the individual behavior of each phase as well as their mutual interactions. The non-matching macro and mesoscopic meshes are attached based on the use of coupling finite elements in the context of the rigid coupling scheme to adequately guarantee the continuity of displacement between both scales. Numerical analyses of dog-bone shape specimens under tensile load and three-point bending beams were performed. The responses obtained numerically show a good agreement with experimental ones found in literature demonstrating how the proposed approach is efficient, robust and useful for modeling crack propagation in HSC.

A smoothed particle hydrodynamics study on effect of coarse aggregate on self-compacting concrete flows

Coarse aggregates increase inhomogeneity and alter rheological properties of self-compacting concrete. In this work, the effect of coarse aggregates on self-compacting concrete is studied by considering its pipe flow. Self-compacting concrete is modelled as suspension of coarse aggregates in cement mortar and a two-phase Smoothed Particle Hydrodynamics (SPH) model is employed. Cement mortar, a yield-stress fluid, is modelled by fluid SPH particles, while each coarse aggregate is represented by a group of solid SPH particles, which moves as a rigid body. Simulation results show that, at the same volume fractions, the flow rate is higher for larger coarse aggregates, that is up to 24% in the investigated cases. Both effective yield stress and effective plastic viscosity of the concretes increase with the coarse aggregate content. Effective yield stress is smaller for bigger coarse aggregates. The reduction in effective yield stress is a consequence of bigger averaged gap between larger coarse aggregates through which the cement mortar flows.

Study on the influence of the shape and size of coarse aggregate on the strength of concrete

Concrete is the largest building material at present, and coarse aggregate as one of the important materials of concrete, its performance will have an important impact on the performance of concrete. Firstly, the effect of coarse aggregate on the length of concrete is analyzed, then the influence of morphology, particle size and content of coarse aggregate on the performance of concrete is analyzed, and the existing problems are pointed out. All these work provide a basis for improving the performance of concrete and lays a foundation for optimizing the mix design.

Effects of coarse aggregates on physical and mechanical properties of C170/185 ultra-high strength concrete and compressive behaviour of CFST columns

The demand for and use of ultra-high strength concrete (UHSC, fck > 90 N/mm2) in high-rise construction have become attractive nowadays, even in countries with seismic activities. However, the poor ductility of it is one of the key concerns leading to the code restrictions on its application even it is infilled into the steel tubes (CFSTs). To study the strength and ductility, this paper presented an experimental work on physical and mechanical properties of UHSC in terms of workability, density, elastic modulus, compressive strength, modulus of rupture and splitting tensile strength; and compressive behaviour of CFSTs using the UHSC, considering the effects of curing age, specimen size, coarse aggregate size and proportion. The test results revealed that the workability of UHSC could be improved by mixing the larger-size coarse aggregates which had little influence on its density; the coarse aggregate size affected the compressive strength in both ways: beneficial and adverse, and the final effect should be determined by its proportion; different from the normal strength concrete (NSC), the UHSC specimens with cylinder shape and larger-size had higher strength than those with cubic shape and smaller-size. It is concluded that, by replacing base material of the UHSC with 38% ordinary coarse aggregates having a maximum size of 10 mm to form the double-tube CFSTs, the ductility can be improved with the axial load capacity not affected.

Compressive and flexural properties of ultra-high performance fiber-reinforced cementitious composite: The effect of coarse aggregate

The inclusion of coarse aggregate in the cementitious composite can improve the mechanical property and simultaneously curb the cement demand thus lowering the production cost in concrete built infrastructure. This study investigates the effects of different coarse aggregate types and contents on the compressive and flexural properties of ultra-high performance fiber-reinforced cementitious composite (UHPFRC). Four types of coarse aggregates (granite, basalt, limestone and steel slag) and four contents denoted by the volume of mortar replacement (0%, 15%, 30% and 40%) are the main variables. The test results have shown a significant increase in compressive strength and elastic modulus of UHPFRC after moderate addition of coarse aggregate with only an expense of a slight reduction in the flexural strength and post-peak ductility. The aggregate types having different stiffness can be effective in either increasing the compressive strength or enhancing the post-peak ductility, which is also true for the increase in aggregate content. With respect to the flexural behavior, it is found that coarse aggregate type significantly affects the flexural strength and equivalent flexural strength ratio, whilst no considerable variations in the first crack strength is observed. Furthermore, an analytical model is proposed to generate the complete compressive stress-strain curves of UHPFRC.

Effects of coarse aggregates on chloride diffusion coefficients of concrete and interfacial transition zone under experimental drying-wetting cycles

Chloride ions diffusion into concrete is one of the most significant factors for reinforced concrete (RC) structures exposed to marine environment, and this can deteriorate reinforcing steel in concrete and cause steel corrosion, ultimately, shorten the durability and serviceability of RC structures. In this paper, the in-door physical experiment method was adopted to explore the effects of natural coarse aggregate on chloride concentration profiles and diffusion behaviors for concrete specimens under man-made exposure condition of drying-wetting cycles. All investigations were based on 10 concrete mixture designs containing variable volume fractions and maximum sizes of natural coarse aggregate for maximum exposure period of 170 days. The chloride profiles versus exposure time, coarse aggregate volume fraction and maximum size were discussed in this paper. The time-dependent model of surface chloride concentration, and the multifactor model of chloride diffusion coefficient of concrete specimens included exposure time, volume fraction, and maximum size of coarse aggregate were developed based on the experimental measurements. In addition, an empirical prediction model for estimating the chloride diffusion coefficient of interfacial transition zone (ITZ) by the consideration of coarse aggregate was determined. Finally, the accuracy and reasonability of the two models of chloride diffusion coefficients for concrete and ITZ considering the effects of coarse aggregate were validated in terms of the meso-scopic finite element numerical simulation method for chloride diffusion into concrete.