Effect of Coarse Aggregate Characteristics on Drying Shrinkage of Concrete (original) (raw)
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ACI Materials Journal, 2005
An experimental program was carried out to determine the influence of concentration and nominal size of coarse aggregate on the development of lateral and pore water pressures of self-consolidating concrete (SCC). Nine mixtures prepared with sand-total aggregate ratios (S/A) varying between 1.0 and 0.30 were evaluated. The mixture made with an S/A value of 0.50 was repeated three times with different coarse aggregate gradations of 10-5, 14-5, and 20-5 mm. An experimental column measuring 2800 mm in height and 200 mm in diameter was used to determine lateral pressure and pore water pressure during the plastic stage of cement hydration. Rheological characteristics were assessed to determine the relationship between internal friction and lateral pressure development.
Variations of Lateral and Pore Water Pressure of Self-Consolidating Concrete at Early Age
ACI Materials Journal, 2004
The granular phase in concrete constitutes more than 60% of its total volume and can have significant influence on the development and variation of lateral pressure exerted by the plastic concrete. This study investigates the kinetics of variations in lateral pressure and pore water pressure that can be exerted by self-consolidating concrete (SCC) during the plastic stage of cement hydration and until the early stage of hardening. Nine mixtures of constant slump flow values of 650 ± 15 mm were evaluated by varying the sand-tototal aggregate ratio R from 1.0 to 0.30. The mixture proportioned with an R value of 0.50 was tested with three different coarse aggregate gradations of 10-5, 14-5, and 20-5 mm. Each concrete was tested to determine setting time, adiabatic heat rise and temperature development, and pressure variations with time. Test results show that the kinetics of lateral pressure drop during the plastic stage are significantly affected by the degree of internal friction that can be related to coarse aggregate concentration. For mixtures with R values greater than 0.50, the concrete behaved as an exclusively viscous material with a limited degree of internal friction, which resulted in greater development of lateral pressure. For mixtures with R values lower than 0.50, the concrete appeared to exhibit greater resistance to shear stress given the higher degree of aggregate friction, which led to considerably lower lateral pressure development. The drop in lateral pressure toward zero occurs after the end of the dormant period as the rate of cement hydration is accelerated. Beyond the dormant period, progressive formation of hydration products leads to the creation of a structural network, and the pore water pressure begins to drop abruptly towards negative values. The time for cessation lateral pressure is shown to be influenced by the R value. For R values greater than or equal to 0.40, the concrete can continue to exert some lateral pressure until the onset of final setting. For mixtures made with R values of 0.36 and 0.30, the cessation of lateral pressure occurred before initial setting as the rate of pressure drop was more accentuated than that resulting from SCC with higher R values.
Effect of various types and sizes of aggregate on self-compacting concrete
IOP Conference Series: Materials Science and Engineering, 2019
Aggregates play important role in concrete; it serves as Structural fillers which are used in concrete production. Aggregate sizes, types and gradation are the most important factor when selecting aggregate. This study examines incorporating different sizes and types of coarse aggregate. Testing rheology and strength of self-compacting concrete mixes at varying sizes and different types of coarse aggregate. The various aggregate sizes used in the Various mixes are 10, 12.5 and 20mm, the types of aggregate used are granite, gravel and ceramic tiles and superplasticizer used is Conplast SP 430 with water cement ratio of 0.45. slump flow test, T50, L-box and V-funnel test were carried out on the various mix to determine the fresh properties of the concrete mix. The mechanical properties (compressive, flexural and split tensile strength test) were conducted on the mixes at different curing age (7, 21 and 28 days). The aggregate size 10mm and granite types had the highest slump flow for ...
Aggregate: A key ingredient of self consolidating concrete
Self-consolidating concrete (SCC) is known to possess the incompatible properties of high flowability together with remarkable stability. Flowability of SCC can easily be achieved by increasing the water content or incorporating proper admixes. But, providing adequate stability is more difficult and requires special attention to mix materials and proportion .
2011
This paper presents the key characteristics of fresh self-compacting concrete (SCC) made of five types of cements and coarse aggregates with different physical properties. The characteristics of SCC are evaluated in terms of viscosity, flowability, passing ability and segregation resistance of fresh concrete as per the European Guidelines for SCC. It is concluded that all key characteristics displayed changes depending on both the type of coarse aggregate and cement. Shape and morphological characteristics of the coarse aggregates like surface texture played significant role on the performance of fresh SCC. Mixes composed of gravel with smooth surface and spherical shape exhibited improved levels of the viscosity, flowability and passing ability of fresh SCC in comparison to crushed coarse aggregates with rough surfaces. Although the relative specific gravity and fineness of the cement influenced the characteristics some other factors can be responsible for the behavior of the SCC a...
The impact of coarse aggregate shape on the behavior of self-compacting high-performance concrete
E3S Web of Conferences, 2018
Self-Compacting High Performance Concrete (SCHPC) presents a crucial step in the development of concrete technology. The most important features of self-consolidating concrete are flowability, segregation resistance and passing ability. Generally, the rheological properties are modified by effective superplasticisers and water to binder ratio. The aim of this study is to focus on the important aspect of the impact of shape of the coarse aggregate on fresh concrete mixture properties, strength and deformability of SCHPC. Coarse aggregate is a significant proportion of the concrete volume and therefore has a meaningful influence on its quality. By appropriate selection of the shape of the grain aggregate, it is possible to affect the rheological parameters of concrete. The results presented in this study indicated that the shape of the grains of coarse aggregate has an impact on the strength and stiffness of SCHPC. Moreover, the occurrence of irregular grains of coarse aggregate cause...
Effect of Clay Fines on the Behavior of Self-Compacting Concrete
The technology of concrete has significantly increased in recent years through the use of superplasticizer and availability of mineral additions. One of the most recent materials used as an additive, replacing a portion of cement in concrete, is fine clay fired at a temperature of 800˚C to 900˚C. This research is based on trials that complied with artificial pozzolan (waste crushed brick), and their effect on the rheological and mechanical behavior of mortar. The addition of 5% of a waste crushed brick has helped not only to improve the strength (tensile and compression), but also to foster a better rheological behavior in terms of fluidity and stability, with a low heat of hydration compared to control. However, tests of optimizing the content of self-compacting concrete (SCC) in coarse aggregates, sand and binder, led us to confirm that the combined mass of more optimal (better workability and stability) is that based on low in volumetric percentage of sand/paste with a granular skeleton richest gravel low dimensions (2/3 of G 3/8 and 1/3 of G 8/15).
Cement and Concrete Research, 2005
A comprehensive research study was carried out to determine the effect of binder type and content on the variations in lateral and pore 10 water pressures that can be exerted by self-consolidating concrete after casting and up to early stages of hardening. Test results show that both 11 physical and chemical phenomena can influence the kinetics of the decrease in lateral pressure until cancellation. The former phenomenon 12 occurs mainly during the dormant period of cement hydration, and is significantly affected by the binder type and content. Regardless of the 13 binder type, the effect of increasing the binder content resulted in sharper drops in pressure. The cancellation of lateral pressure depends on a 14 chemical effect and occurs after the end of the dormant period when the rate of cement hydration is accelerated. Beyond the dormant period, 15 the progressive formation of hydration products leads to the creation of a structural network, and the pore water pressure begins to drop 16 abruptly towards negative values.
A study on the performance of lightweight self-consolidated concrete
This paper presents a study on the fresh and hardened characteristics of lightweight aggregate concrete incorporating self-compacting agent (LWSCC). Self-compacting agent (SCA) (a polycarboxylic-based superplasticiser in combination with a viscosity modifying admixture) and local-produced lightweight aggregate (LWA) produced from expanded clay type were utilised. Various LWSCC mixes made with different mix proportions, namely dosage of self-compacting agent, water/cement ratio, LWA/sand ratio and normal weight aggregate as a partial replacement of LWA, were prepared. The initial slump flow, rate of slump flow loss and air content were then performed to assess the fresh properties of LWSCC. Twenty-eight day compressive strength, ultrasonic pulse velocity, porosity and density were determined for investigating the hardened properties of LWSCC. The results reveal that, by using locally produced materials, it is possible to manufacture a structural LWAC with low density and high selfconsolidating characteristics (flowability, deformability and stability). Both fresh and hardened characteristics of LWSCC are mainly controlled by dosage of a SCA, where the flowability, self-compactability, strength, homogeneity and porosity of LWSCC can be enhanced with increasing SCA content up to certain dosage of SCA (0.80), at which all these characteristics would start to decline with increasing SCA content. However, LWSCC loses its fresh parameters rapidly with increasing the dosage of SCA and lightweight aggregate/sand ratio. The results also showed that the compressive strength, homogeneity and porosity of LWSCC could be significantly improved by reducing the ratio of w/c and LWA/sand ratio, and utilising normal-weight aggregate in LWSCC mixes.