Increase Of Maximum Aggregate Size Research Articles

Effect of Maximum Aggregate Size and Powder Content on the Properties of Self-compacting Recycled Aggregate Concrete

The utilization of recycled aggregates and various industrial by-products is considered a sustainable strategy in the concrete industry. In this study, the effect of the maximum size of recycled coarse aggregate and the cementitious binder content on fresh and hardened properties of self-compacting concrete was investigated. Self-compacting concretes with maximum aggregate sizes of 9.5 mm, 12.5 mm, and 19 mm were prepared at water-to-binder ratios of 0.39, 0.42, and 0.45, respectively. For all mixtures, 100% recycled aggregate was used as coarse aggregate and 60% of cement was replaced by industrial by-products, i.e., fly ash and ground granulated blast furnace slag. The tests included slump flow, air content, hardened density, compressive strength, elastic modulus, and splitting tensile strength. The results showed that the increase in maximum aggregate size and binder content tended to improve both fresh and hardened properties of self-compacting concrete.

Effects of content and size of aggregate on the mechanical responses of concrete at cryogenic temperatures

The meso-structure of concrete, which determines its apparent performance, is closely related to the maximum aggregate size (MAS) and aggregate volume. At cryogenic temperatures, due to the freezing of pore water, the internal structure of concrete is changed, leading to some difference in the role of coarse aggregate particles. In this study, the meso-mechanical modeling method was adopted based on the continuous grading aggregate model to investigate the influence of content and size of aggregate at cryogenic temperatures. The uniaxial compressive and uniaxial tensile behavior of concrete cubic specimens (sized by 150 × 150 × 150 mm3) with various aggregate volumes (15 % ∼ 45 %) and MAS values (12 mm ∼ 36 mm) were simulated with consideration of cryogenic temperatures effects. The variation of compressive strength, tensile strength, elastic modulus, and fracture to energy with maximum aggregate size and aggregate volume fractions at cryogenic temperatures was investigated, and the related influencing mechanism was analyzed. The numerical results demonstrated that the failure patterns of specimens at cryogenic temperature show some differences compared with those at ambient temperature. Besides, it was indicated that the effect of maximum aggregate size and aggregate volume on the elastic modulus and the energy to fracture is consistent with those at ambient temperature. At cryogenic temperatures, the compressive strength is improved with the increase of maximum aggregate size. For the smaller aggregate volume fraction (15 % ∼ 30 %), the tensile strength at cryogenic temperatures tends to increase as the increase of maximum aggregate size, while an opposite trend appeared at larger aggregate volume. Additionally, as the increase of aggregate volume fractions, the compressive strength decreases first and then increases at cryogenic temperatures, while the tensile strength and elastic modulus exhibit a trend of increase. It is concluded that cryogenic temperatures can enhance the influence of maximum aggregate size on tensile strength, but weaken the influence of aggregate volume fractions on strengths.

Strength and fracture properties of roller compacted concrete (RCC) prepared by an in-situ compaction procedure

The use of roller compacted concrete (RCC) technology in pavement applications has been steadily increasing owing to its economical as well as practical advantages. Past literature studies on RCC mixtures, focused mainly on the effects of RCC mixtures on their strength and durability properties, and there is a lack in the fracture properties. In this experimental study, a total of seven different RCC mixtures were designed with four different binder ratios ranging from 200 kg/m3 to 600 kg/m3, and two different aggregate gradations with maximum aggregate sizes of 12 mm and 19 mm to investigate the effect of mixture design on RCC mechanical performance and fracture properties. All RCC mixtures were compacted in a plate mold with dimensions of 15x85x200 cm3 by applying first a vibratory plate compactor, then a double drum vibratory hand roller to simulate the actual field compaction procedures. Cores and prismatic beam specimens were taken from the plates to determine the strength and fracture properties of RCC mixtures. Single-point bending test was applied on the notched beams to determine the fracture parameters by using RILEM procedure based on the non-linear two parameter fracture model. According to the statistical analysis results, it was found that the strength and the fracture properties of RCC mixtures were affected not only by the mixture proportions but also by the compaction amount. Moreover, it was shown that the critical stress intensity factor (KIc) was enhanced with the increase of maximum aggregate size, compaction ratio, then binder dosage. On the other hand, critical crack tip opening displacement, CTODc seems to be affected only by the fine to total aggregate ratio or the maximum aggregate size.

Effects of maximum size of brick aggregate on properties of concrete

Effects of maximum aggregate size (12.5mm, 19.0mm, 25.0mm, 37.5mm, and 50.0mm) on properties of concrete made with different sand to total aggregate volume ratio (0.40 and 0.45), W/C ratio (0.45, 0.50, and 0.55), and cement content (375kg/m3 and 400kg/m3) were investigated. Considering the variables, a total of 552 concrete cylinder specimens of diameter 100mm diameter and height 200mm were made for 52 numbers of independent cases. Brick aggregates were tested for specific gravity, absorption capacity, unit weight, and abrasion resistance. Concrete specimens were tested for compressive strength, stress-strain curve, splitting tensile strength, and Young's modulus. Results have revealed that for higher cement content (400kg/m3), concrete made with small aggregates give more compressive strength. However, for a cement content of 375kg/m3, and W/C ratio of 0.45, the compressive strength is increased with an increase in maximum aggregate size up to 37.5mm. The compressive strength of concrete increases with an increase in s/a ratio from 0.40 to 0.45. Relationships between mechanical properties of concrete, and stress-strain relationships are proposed for different maximum aggregate sizes.

Effects of maximum aggregate size on UPV of brick aggregate concrete

Investigation was carried out to study the effects of maximum aggregate size (MAS) (12.5mm, 19.0mm, 25.0mm, 37.5mm, and 50.0mm) on ultrasonic pulse velocity (UPV) of concrete. For investigation, first class bricks were collected and broken to make coarse aggregate. The aggregates were tested for specific gravity, absorption capacity, unit weight, and abrasion resistance. Cylindrical concrete specimens were made with different sand to aggregate volume ratio (s/a) (0.40 and 0.45), W/C ratio (0.45, 0.50, and 0.55), and cement content (375kg/m3 and 400kg/m3). The specimens were tested for compressive strength and Young’s modulus. UPV through wet specimen was measured using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). Results indicate that the pulse velocity through concrete increases with an increase in MAS. Relationships between UPV and compressive strength; and UPV and Young’s modulus of concrete are proposed for different maximum sizes of brick aggregate.

Analytical solution for Young's modulus of concrete with aggregate aspect ratio effect

This paper presents an analytical solution for Young's modulus of concrete with the aggregate aspect ratio effect. By taking the interfacial transition zone (ITZ)-coated aggregate as an ‘equivalent aggregate', the three-phase concrete is reduced to a two-phase composite material. The interaction direct derivative estimate is then adopted to derive an analytical solution for Young's modulus of concrete. After the validity of the analytical solution is verified with three sets of experimental results, the effects of various key factors on Young's modulus of concrete are evaluated quantitatively. The numerical results indicate that Young's modulus of concrete increases with an increase in maximum aggregate size, aggregate aspect ratio and Young's modulus of the aggregate, but decreases with increasing ITZ thickness. It is also found that the aggregate gradation has a certain influence on Young's modulus of concrete.

천연모래 치환율과 경량 굵은 골재 최대 크기에 따른 경량 골재 콘크리트의 역학적 특성

The effect of the maximum aggregate size and substitution rate of natural sand on the mechanical properties of concrete is evaluated using 15 lightweight aggregate concrete mixes. For mechanical properties of concrete, compressive strength increase with respect to age, tensile resistance, elastic modulus, rupture modulus, and stress-strain relationship were measured. The experimental data were compared with the design equations specified in ACI 318-08, EC2, and/or CEB-FIP code provisions and empirical equations proposed by Slate et al., Yang et al., and Wang et al. The test results showed that compressive strength of lightweight concrete decreased with increase in maximum aggregate size and amount of lightweight fine aggregates. The parameters to predict the compressive strength development could be empirically formulated as a function of specific gravity of coarse aggregates and substitution rate of natural sand. The measured rupture modulus and tensile strength of concrete were commonly less than the prediction values obtained from code provisions or empirical equations, which can be attributed to the tensile resistance of lightweight aggregate concrete being significantly affected by its density as well as compressive strength.

Aggregate interlock in lightweight concrete continuous deep beams

There are very few, if any, available experimental investigations on aggregate interlock capacity along diagonal cracks in lightweight concrete deep beams. As a result, the shear design provisions including the modification factor of ACI 318-08 and EC 2 for lightweight concrete continuous deep beams are generally developed and validated using normal weight simple deep beam specimens. This paper presents the testing of 12 continuous beams made of all-lightweight, sand-lightweight and normal weight concrete having maximum aggregate sizes of 4, 8, 13 and 19 mm. The load capacities of beams tested are compared with the predictions of strut-and-tie models recommended in ACI 318-08 and EC 2 provisions including the modification factor for lightweight concrete. The beam load capacity increased with the increase of maximum aggregate size, though the aggregate interlock contribution to the load capacity of lightweight concrete deep beams was less than that of normal weight concrete deep beams. It was also shown that the lightweight concrete modification factor in EC 2 is generally unconservative, while that in ACI 318-08 is conservative for all-lightweight concrete but turns to be unconservative for sand-lightweight concrete with a maximum aggregate size above 13 mm. The conservatism of the strut-and-tie models specified in ACI 318-08 and EC 2 decreased with the decrease of maximum aggregate size, and was less in lightweight concrete deep beams than in normal weight concrete deep beams.

Concrete Shrinkage-Induced Damage Taking into Account Aggregate Restraint

The influence of concrete meso-structure and coarse aggregate size on early age crack is studied. In this study, concrete is regarded as a three-phase material based on shrinkage property. The mortar matrix and interfacial transition zones undergo shrinkage and no spherical coarse aggregate particles are considered to restain the shrinkage by particle interaction. The results show that concrete meso-structure plays an important role in the safety of concrete, different aggregate distribution in concrete leads to different initial cracks and propagation due to shrinkage. With the increase of maximum aggregate size, the value of shrinkage deformation becomes unstable and varies in a wide range; relevant shrinkage cracking becomes easier too.

Effect of fracture path on the fracture energy of high-strength concrete

Abstract The paper indicates that there may not exist a direct relationship between fracture energy and compressive strength. The fractal theory is used to quantitatively study the fracture surface and the relationship between fracture energy and fracture characteristics. The test results show that fractal dimension increases with the increase of maximum aggregate size. For the concrete with higher water–binder ratio, fractal dimension increases more rapidly than that for the concrete with lower water–binder ratio. For the same water–binder ratio, fracture energy of concrete increases with the increase of fractal dimension. Fracture energy for lower water–binder ratio increases with fractal dimension more rapidly than that for higher water–binder ratio. The ductility index is used to assess the brittleness of concrete. There exists a good lineal correlation between ductility index and fractal dimension for all test series. Thus, fractal dimension can be used as a parameter to characterize the brittleness of concrete.