Papers by Keyword: Autogenous Shrinkage

Abstract: The effects of steel slag with 0, 10%, 20 % and 40% content on the chemical shrinkage, autogenous shrinkage, internal relative humidity, and drying shrinkage of calcium sulfoaluminate cement paste were studied. The results show that the compressive strength of calcium sulfoaluminate cement paste at an early stage decreases gradually when the content of steel slag increases. When the steel slag content is 0 and 10%, the compressive strength of hardened cement pastes gradually decreases at 90 and 180 days, but the samples with steel slag content of 20% and 40% maintain the compressive strength growth within 180 d. With the extension of curing period, the gap of compressive strength is gradually narrowed. The autogenous shrinkage decreases with the increase of steel slag content and has a good linear relationship with the relative humidity inside the paste. The proportion of autogenous shrinkage to chemical shrinkage is deficient, and most chemical shrinkage occurs in the form of the pore volume. Although the trends of drying shrinkage and autogenous are consistent, the former is more severe than the latter.

Abstract: The cement-silica fume blended pastes were prepared with different silica fume (SF) dosages of 0%, 5%, 10%, and 15% at different water-binder ratios (W/B) of 0.4 and 0.5. The autogenous shrinkage (AS) and the drying shrinkage (DS) of the paste samples in the hydration period of 7d (168 hours) were measured by a new measurement technique to explore the influence of W/B and silica fume incorporation on the shrinkage in early age. The study results can provide reference for high performance concrete mix design.It is found that ether the AS or the DS of the paste samples shows a similar pattern, and the AS development with hydration time appeared a temporary expansion period after a rapid growth, especially in the samples at a higher W/B or with a lower SF content. However, the DS development did not occur obvious expansion period.Three development trends were obtained for the factors of W/B and SF content. 1) the AS and DS of the pastes mainly occurred in early ages. The lower W/B, the shorter the rapid growth periods, and the higher the shrinkage ratio of 1d to 7d. For the pastes with W/B of 0.4, the AS grew rapidly in 1d and the DS grew rapidly in the first 10h, and the AS value in 1d reached to 63.6% of 7d, and the DS value reached to 62.1% of 7d in the paste with SF of 10%. For the pastes with W/B of 0.5, the rapid growth periods of the AS and DS respectively extended to 30~33h and 12h, and the AS value in 1d reached to 60.0% of 7d, and the DS value reached to 57.2% of 7d in the paste with SF of 10%. 2) The lower W/B, the higher the shrinkage ratio of the AS to the DS. When the SF dosage is 10%, the ratio of the AS value to the DS value of 7d is 21.66%~21.15% for W/B of 0.4, and only 6.06%~5.78% for the W/B of 0.5. 3) the higher SF content results in the higher AS in cement-SF blended pastes. For the pastes with W/B of 0.4, the ratio of the AS to the DS increased from 6.98% to 30.16% with the increase of content of SF from 5% to 15% in 1d, from 15.1% to 28.19% in 3d, from 16.78% to 26.16% in 7d.

Abstract: The effect of calcinations time on carbon content and grinding time on fineness of rice husk ash (RHA) has studied. The influence of workability, compressive strength, autogenous shrinkage and early anti-cracking behavior of pretreatment RHA with calcined 30min-grinded 30min-pre-wet as admixture to UHSC has researched, the result shows that, when the content of cement replaced by RHA is 10%, the workability and compressive strength change little, while the autogenous shrinkage of UHSC reduce by 28.3%, and early anti-cracking grade increase from III to IV.

Abstract: Durability in High Performance Concrete have resulted in the development of admixtures to mitigate several concrete deterioration mechanisms. Due to the low water/binder, HPC enables autogenous shrinkage that could lead to cracks at early ages. Superabsorbent polymers, shrinkage reducing admixtures and corrosion inhibitor based on calcium nitrite were used in HPC with silica fume to evaluate autogenous shrinkage. SAP was added with an amount of intenal curing water determined by the modification proposed by Jensen to the Power’s Model. Results showed that admixtures could improve or aggravate autogenous shrinkage.

Abstract: Influence of fiber on workability and mechanical property of ultra-high strength concrete (UHSC) were studied. Results show that, when amount of steel fiber (Equivalent diameter is 0.2mm; nominal length is 13mm; Tensile strength is 2850MPa )substituting fine aggregate is 120kg/m³, UHSC could have the best mechanical properties of 139.0MPa compressive strength, 18.0MPa flexural strength, and 10.0MPa Splitting strength; steel fiber cannot improve volume stability of UHSC.

Abstract: High performance concrete (HPC) consisting of low water-binder (w/b) ratio and supplementary cementitious materials (SCM) is more prone to shrinkage cracking if subjected to external deformation restraint. The effectiveness of using lightweight fine aggregate (LWA) for autogenous shrinkage reduction is being studied along with implications on salt frost durability. HPC consisting of 0.33 w/b ratio and cementitious replacement level up to 50% by slag cement and natural sand replacement level by LWA of up to 50% is investigated. Results indicate that these concretes exhibit excellent salt frost resistance provided the HPC is sufficiently air entrained. The mitigation of autogenous shrinkage by LWA is analyzed by comparing the spacing of LWA particles in cement paste and the flow distance of retained moisture in LWA to the adjacent paste.

Abstract: This paper presents an investigation of the effect of emulsified waste cooking oil on the porosity, EDEX results and the reduction of autogenous shrinkage of the high strength concrete with W/B of 20% incorporating 20% of fly ash and 10% of silica fume. Two different types of shrinkage reducing agents, the existing glyeol based shrinkage reducing agent (SR) and the waste cooking oil (WCO) were applied and compared. The effect of emulsification of the WCO with two emulsifying speeds, 2000 rpm and 4000 rpm were also investigated. It is found that the emulsified WCO has desirable shrinkage reduction effect than un-emulsified WCO and existing SR. Test results also indicated that emulsified WCO could also reduce pore volume due to saponification reaction

Abstract: The effect of modified metakaolin (MMK) on the evaporable water and chemically bound water content of hardened cementitious materials have been investigated. Concrete specimens with 0%, 4%, 7% and 10% of MMK were included. Metakaolin was pre-modified in order to increase the dispersion and contact angle, which might further improve the workability of the concrete. The experimental results showed that both the evaporable water and bound water were increased with the increasing of the MMK content. MMK has a special layered structure. Water can get into the layers through this special layer during the mixing of concrete specimens. Part of MMK with water between the layers didn’t participate in the hydration reaction at the early stage of the hydration, which increased the evaporable water of the cementious materials. The water absorbed in MMK will be released to promote the formation of hydration products and thus the chemically bound water content will increase continuously at the later stages. It also reduced the autogenous shrinkage of the specimens which caused by the decrease of water in capillary pores at low water cement ratio (0.3).

Abstract: Early-age autogenous shrinkage is key problem of high performance concrete. It can cause a lot of early-age cracks in concrete structure and further endanger the permeability and durability. Adding expansion agent can control the early-age autogenous shrinkage strain and reduce the risk of early-age cracks. In this paper, the early-age autogenous shrinkage stress of concrete cube is calculated. The results show that, early-age autogenous shrinkage stress is larger than early-age tensile strength of concrete. So some cracks occur on the surface of concrete structure. By adding expansion agent, the early-age autogenous shrinkage strain and stress both decreases.

Abstract: The influence rules of the mineral admixtures containing fly ash, ground slag and silica fume on the early-age autogenous shrinkage of high-performance concrete have been discussed in this paper. According to the research results, fly ash mixture can substantially decrease the early-age autogenous shrinkage of high-performance concrete, while the silica fume will increase the autogenous shrinkage. Meanwhile the influence of ground slag on autogenous shrinkage is related to its fineness and admixture amount. Generally, it is believed that when the fineness of the fly ash is higher than 4000cm2/g, the autogenous shrinkage will increase with the increasing admixture amount. The double admixture or multi-admixture of fly ash or ground slag is better for reducing the early-age autogenous shrinkage of concrete than the single-admixture. The early-age autogenous shrinkage of concrete occurs in distinctive linear dependence with the three types of mineral admixtures.