Effect Of Aggregate Content Research Articles

Time-varying analytical model and mesoscopic numerical simulation of chloride ion diffusion in prestressed concrete cylinder pipe

In this paper, a time-varying analytical model for chloride ion diffusion in Prestressed Concrete Cylinder Pipe (PCCP) protective layer is established based on the separation of variables method and Bessel function. The model takes into account factors such as steam curing, pipe radius, curing age, and exposure time. Meanwhile, the mesoscopic numerical simulation is conducted on the chloride ion diffusion behavior in the PCCP protective layer, and the effects of aggregate content, interfacial transition zone (ITZ) volume fraction, and ITZ chloride ion diffusion coefficient on chloride ion diffusion are analyzed. Results show that the aggregate has inhibitory effect on the diffusion process of chloride ions, without considering the influence of ITZ. As the aggregate content increases, the average depth of chloride ion diffusion decreases linearly. In the event of both the influence of aggregate content and ITZ are considered, there is a competitive relationship between the two. The larger the diffusion coefficient of chloride ions in ITZ, the larger the average diffusion depth of chloride ions is. In addition, the correctness of the numerical model and analytical model is compared and verified by combining their calculation results. Compared with traditional chloride ion diffusion models, the smaller the pipe diameter, the more accurately the chloride ion diffusion law can be reflected by the analytical model.

Effects of Aggregate Content on Rheological Properties of Lubrication Layer and Pumping Concrete

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Effect of aggregate content on the CFRP-concrete effective bond length: An experimental and analytical study

Despite the wide range of proposed models in construction codes for estimating the carbon fiber reinforced polymer (CFRP)-concrete effective bond length, no attention has yet been given in the codes regarding the effect of aggregate content on effective bond length. The current study investigated the above-mentioned issues with varying volumes of coarse aggregates based on the concept of ‘sand ratio’ defined as the ratio of fine aggregate volume-to-total aggregates’ volume in concrete. For this purpose, 52 single-lap shear tests were conducted in two main groups of 23 and 35 MPa compressive strengths of concrete. Analytical and experimental results revealed that the effective bond length increased by 54% by increasing the sand ratio from 0.34 to 0.70 for the first group. However, the effective bond length demonstrated a 26% reduction by increasing the sand ratio from 0.70 to 1.00. Regarding the second group, the effective bond length increased by 45% by increasing the sand ratio from 0.29 to 0.62, while the effective bond length represented a 40% decrease by increasing the sand ratio from 0.62 to 1.00. Finally, the results indicated the necessity of correction factors in code models to explain the sand ratio effect. Such correction factors were extracted to be applied to the code models.

Hybrid steel/glass fiber-reinforced self-consolidating concrete considering packing factor: Mechanical and durability characteristics

This study intends to determine the effect of fiber type and aggregate content on hardened and durability properties of self-consolidating concrete. Steel, glass, and steel/glass hybrid fibers are tested in the present experimental program. Additionally, the effect of aggregate content is considered by using different packing factors and sand-to-all aggregate ratios. Moreover, normal and high strength concrete grades are prepared. Compressive, splitting tensile, flexural, and impact tests are conducted for measuring hardened properties of concrete mixtures. Absorption, desorption, acid attack, resistivity, potential, and chloride diffusion are also durability tests carried out in the present study. Results show that 1.0% and 0.05% are the optimal dosage of steel and glass fibers respectively. Results show that packing factor plays a major role in mechanical characteristics of fiber-reinforced self-consolidating concretes so that an optimal value of 1.12 and 1.14 is obtained for mechanical properties. Also, experimental results reveal that for 1.12 packing factor, the sand-to-all aggregate ratio needs to be equal to the value of 0.50, while 0.57 is achieved as an optimum value for packing factor of 1.14. Overall, results show that hybrid-reinforced self-consolidating concrete is promising for mechanical and durability performance as compared to other mixtures.

Properties and durability of alkali-activated ladle slag

This paper examines the durability of alkali activated ladle slag mortars. Ladle slag, currently an under-utilized crystalline metallurgical by-product, is a promising raw material for alkali activation. However, there is no information about the durability of this material. The aim of this study is to investigate the durability of the alkali activated ladle slag mortar and the effect of aggregate content on the properties. The mechanical strength tests were carried out at 7, 28, 56 and 90 days. In addition, the samples were subjected to drying shrinkage, freeze–thaw, and water absorption tests. Furthermore, the reaction products conversion related to the strength properties were also analysed through thermal analysis. Overall, significant strength and durability properties was attained and significantly influenced by the mix design.

Effect of Aggregate Content on the Concrete Compressive Strength - Ultrasonic Pulse Velocity Relationship

This paper investigates the relationship between the ultrasonic pulse velocity (UPV) and the compressive strength of concrete. The specimens used in the study were made of concrete with varied aggregate contents from 1000 to 1400 kg/m3. The specimens were made and tested at the Hawler Construction Laboratories (HCLabs) in Erbil, Kurdistan Region of Iraq. The UPV measurement and compressive strength tests were carried out at the concrete age of 28 days. The experimental results show that the relationship between UPV and the compressive strength of concrete is significantly influenced by the coarse aggregate content. Relationships are established for the range of contents of coarse aggregates and discussed.

Deflection-hardening hybrid fiber reinforced concrete: The effect of aggregate content

High Performance Fiber Reinforced Concretes (HPFRC) are emerging materials with superior mechanical properties accounting for crack occurrence and propagation under excessive tensile loads along with the many commonly encountered durability issues. One drawback of such materials is the restricted size and amount of coarse aggregates used in mixtures incorporating single or hybrid fibers (in most cases). This, therefore, increases the amount of binder resulting in higher cost, dimensional instability and cracking potential (especially at early ages). In this study, HPFRC mixtures with a maximum aggregate size of 12mm were developed with maximal variation in coarse aggregate contents without compromising deflection-hardening behavior. Three different fibers were used at a maximum of 2% of volume in single or hybrid systems: polyvinyl-alcohol (P), hooked-end steel (S) and nylon (N) fibers. To function synergistically with different fiber types and high amounts of coarse aggregates, matrix properties were optimized by varying the proportions of fly ash to Portland cement (FA/PC ratios of 0.20, 0.45, and 0.70, by weight) and aggregate to binder (A/B ratios of 1.0, 1.5, and 2.0, by weight). Experimental results showed that a deflection-hardening response can be obtained from HPFRC mixtures with single or hybrid fiber systems regardless of the FA/PC ratio, A/B ratio, and initial curing age selected without endangering the compressive and flexural strength results. It is believed that production of hybrid fiber composite mixtures with high concentrations of coarse aggregates and industrial by-products can contribute to superior mechanical and durability performance, enhanced greenness, as well as the widespread usage of such materials in the field at a reasonable price compared to their counterparts.

Determining the steady-state chloride migration coefficient of ITZ in mortar by using the accelerated chloride migration test

In this study, an electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. The steady-state chloride migration coefficient of mortar was determined experimentally as a function of the aggregate volume fraction to investigate the effect of aggregate content. The influence of the aggregate–cement paste interfacial transition zone (ITZ) on the steady-state chloride migration behavior in mortar was investigated using a three-phase model. The three-phase material was composed of cement paste matrix, aggregate, and ITZ. The chloride diffusion is considered to take place in the cement paste and the ITZ phases. The chloride flow is controlled by dilution in the cement paste, and the chloride flow is controlled by the combining effects of tortuosity and dilution in the ITZ. The experimental results are fitted with the three-phase model. Based on the experimental and regression analytical results, the approximate chloride migration coefficient of ITZ with different assumed thicknesses of ITZ is determined.

Properties of fly ash geopolymer concrete designed by Taguchi method

This paper presents an optimization of fly ash geopolymer mixtures by Taguchi method, and a study on the mechanical properties and durability of concrete produced from the optimal mixes. A total of nine mixtures were evaluated by considering the effects of aggregate content, alkaline solution to fly ash ratio, sodium silicate to sodium hydroxide ratio, and curing method. Ordinary Portland Cement (OPC) concrete of 55MPa strength was used as a control mix. Three optimal mixtures (T4, T7 and T10) were identified. Results show that the geopolymer concrete can be produced with of 55MPa at 28days. They had higher tensile and flexural strength, produced less expansion and drying shrinkage, and showed moduli of elasticity that were 14.9–28.8% lower than those of the OPC control mix. The compressive strength of all geopolymer mixtures changed significantly at each wetting–drying cycle, but the weight losses were higher than that of the OPC concrete. Half-cell potential measurement showed that the geopolymer mixes were generally more prone to corrosion, although showed low-level corrosion activity and exhibited times to failure that were 3.86–5.70 times longer than those of the OPC concrete. The test results confirmed that the mechanical properties of the geopolymer mixtures tested are competitive with those of OPC concrete and provide a more durable alternative to the OPC concrete in a seawater environment.

Experimental study on the effect of aggregate content on fracture behavior of concrete

Effect of aggregate content on fracture behavior of concrete is studied by testing on 48 geometrically similar three-point bend concrete beams. The results are analyzed by using a size effect method, in which the fracture behavior of concrete is characterized by two parameters: fracture energy G f and effective fracture process zone c f. Test results showed that with increasing volume fraction of aggregate in the range 45–75%: (1) the compressive strength of concrete decreases slightly (15%), and can be practically considered to be a constant; (2) fracture energy G f varies within 25%, and there is not critical volume fraction which gives the maximum G f; and (3) the size of the fracture process zone decreases, which may be explained by the change in coarseness of grain structures defined in terms of mosaic patterns.

APPROXIMATE ELASTIC MODULI OF LIGHTWEIGHT AGGREGATE

This study presents a method for the estimation of the elastic modulus of lightweight aggregate. In order to investigate the elastic modulus of aggregate and the effect of aggregate content on the elastic modulus of lightweight concrete, cylindrical specimens with different volume ratios (volume ratio of coarse aggregate/total aggregate) and various water/cement ratios were cast and tested. Both single inclusion and double inclusion models were applied to predict the elastic moduli of two-phase and three-phase cement-based composite materials, respectively. The elastic moduli of sand and coarse aggregate were derived from the experimental results using the theoretical models. © 1997 Elsevier Science Ltd

Ultimate Drying Shrinkage of Concrete--Influence of Major Parameters

The effect of aggregate content and elastic modulus on ultimate drying shrinkage of concrete was investigated. A shrinkage model developed by one of the authors that includes these parameters was tested. The model showed excellent agreement with experimental results. Further, the effect of water-cement (w/c) ratio, curing time, and aggregate content on the drying shrinkage versus relative humidity curves in the relative humidity range of 0 to 100 percent was investigated for miniature paste and mortar specimens. For these specimens the relative humidity correction factor was found to be independent of w/c ratio, curing time, and aggregate content in the relative humidity range of 11 to 100 percent and was best described by two linear relationships. The two relationships for the relative humidity correction factor in the relative humidity range of 11 to 50 percent and 50 to 100 percent was characterized by different slopes. Using the relative humidity correction factor and the shrinkage model, ultimate shrinkage of concrete can be estimated at any relative humidity between 11 and 100 percent.