Autogenous Shrinkage Of Concrete Research Articles

The combined effect of steel fiber and MgO on the deformation and mechanical properties of high-strength concrete

Shrinkage cracking of concrete is one of the main problems affecting the durability of high-strength concrete. One of the main measures to solve this problem is to use expansion agents to compensate for the shrinkage of concrete. But on the other hand, excess expansion, while compensating for shrinkage, is likely to have a detrimental effect on mechanical properties of concrete. Especially for bridge decks and airport pavement with high requirements for impact resistance, toughness, and crack resistance, the use of expansion agents alone cannot meet the performance requirements. In this study, the mechanical properties and autogenous shrinkage of concrete were studied when MgO expansion agent (MEA) and steel fiber were used simultaneously. The results showed that the expansion produced by MEA increased the porosity while compensating for the shrinkage of concrete. Compared with plain concrete, the porosity increased by 4.4% when MEA was incorporated alone. After MEA and steel fiber were used simultaneously, the steel fiber constrained the expansion of MEA through the adhesive friction between fiber and matrix, which made the interface transition zone (ITZ) between cement paste and fiber densified. In this way, the shrinkage of concrete was avoided without reducing the mechanical properties. Especially when 8% MEA and 1% steel fiber were used simultaneously, the compressive strength and splitting tensile strength of concrete were increased by 20.6% and 65.0% respectively, and the porosity was decreased by 20.9%. The expansion of concrete at 410d when used simultaneously was 371 × 10−6, which was 20.7% lower than that of MEA alone, avoiding the possible adverse effects of excessive expansion of MEA. The research results have guiding significance for improving the crack resistance and impact resistance of concrete.

Effect of the Water-Binder Ratio on the Autogenous Shrinkage of C50 Mass Concrete Mixed with MgO Expansion Agent

The high adiabatic temperature rise and low heat dissipation rate of mass concrete will promote rapid hydration of the cementitious material and rapid consumption of water from the concrete pores, which may significantly accelerate the development of concrete autogenous shrinkage. In this study, the effect of the water-binder ratio on the autogenous shrinkage of C50 concrete mixed with MgO expansion agent (MEA) was explained with respect to mechanical properties, pore structure, degree of hydration, and micromorphology of the concrete based on a variable temperature curing chamber. The results show that the high temperature rise within the mass concrete accelerates the development of early (14 d) autogenous shrinkage of the concrete, and that the smaller the water-binder ratio, the greater the autogenous shrinkage of the concrete. With the addition of 8 wt% MEA, the autogenous shrinkage of concrete can be effectively compensated. The larger the water-binder ratio, the higher the degree of MgO hydration, and in terms of the compensation effect of autogenous shrinkage, the best performance is achieved at a water-binder ratio of 0.36. This study provides a data reference for the determination of the water-binder ratio in similar projects with MEA.

Prediction of Autogenous Shrinkage of Concrete Incorporating Super Absorbent Polymer and Waste Materials through Individual and Ensemble Machine Learning Approaches.

The use of superabsorbent polymers, sometimes known as SAP, is a tremendously efficacious method for reducing the amount of autogenous shrinkage (AS) that occurs in high-performance concrete. This study utilizes support vector regression (SVR) as a standalone machine-learning algorithm (MLA) which is then ensemble with boosting and bagging approaches to reduce the bias and overfitting issues. In addition, these ensemble methods are optimized with twenty sub-models with varying the nth estimators to achieve a robust R2. Moreover, modified bagging as random forest regression (RFR) is also employed to predict the AS of concrete containing supplementary cementitious materials (SCMs) and SAP. The data for modeling of AS includes water to cement ratio (W/C), water to binder ratio (W/B), cement, silica fume, fly ash, slag, the filer, metakaolin, super absorbent polymer, superplasticizer, super absorbent polymer size, curing time, and super absorbent polymer water intake. Statistical and k-fold validation is used to verify the validation of the data using MAE and RMSE. Furthermore, SHAPLEY analysis is performed on the variables to show the influential parameters. The SVM with AdaBoost and modified bagging (RF) illustrates strong models by delivering R2 of approximately 0.95 and 0.98, respectively, as compared to individual SVR models. An enhancement of 67% and 63% in the RF model, while in the case of SVR with AdaBoost, it was 47% and 36%, in RMSE and MAE of both models, respectively, when compared with the standalone SVR model. Thus, the impact of a strong learner can upsurge the efficiency of the model.

Effect of magnesia expansion agent with different activity on mechanical property, autogenous shrinkage and durability of concrete

The addition of Magnesia Expansion Agent (MEA) to reduce shrinkage of concrete has attracted attention gradually. In this study, three types of MEA with different activity, i.e. R, M, and S were added into concrete by 5% weight of cement. The effects of MEA on hydration, mechanical properties, shrinkage and durability of concrete were comprehensively evaluated. The results indicated that MEA has a certain delaying effect on hydration of cement and the effect is related to its activity. The addition of MEA exhibites a larger porosity at early curing age leading to negative effects on the mechanical properties of concrete. Later, the microstructure of concrete is refined due to the micro-expansion of MEA. As a result, the mechanical strength of concrete increases 5–20 % at 84 d. Meanwhile, the autogenous shrinkage of concrete with MEA of type R, M, and S decreases by 47.6 %, 49.7 %, and 23.8 % at 90 d, respectively. Because of the smaller MPPD and lower porosity, concrete with MEA of higher activity presents better resistance to chloride penetration. In addition, the models of shrinkage and chloride diffusion coefficient of concrete with MEA of different activity were proposed and verified, which can be used in the shrinkage and service life prediction of concrete with MEA. Furthermore, with the increase of MEA activity, the frost resistance of concrete decreases. On the contrary, the lower the MEA activity, the lower the sulfate resistance of concrete.

Effect of water‐to‐cement ratio on internal relative humidity and autogenous shrinkage of early‐age concrete internally cured by superabsorbent polymers

AbstractSelf‐desiccation is one common phenomenon of concrete with low water‐to‐cement (w/c) ratios, which may lead to the decrease of internal relative humidity (IRH), and therefore causing autogenous shrinkage (AS). Superabsorbent polymers (SAPs) are used as a kind of internal curing material to mitigate AS of concrete. The IRH and AS are significantly affected by the w/c ratio, and several attempts have been made to investigate the IRH or AS of concrete with different w/c ratios. However, the prediction model of AS considering IRH and w/c ratio of internally cured (IC) concrete is limited. In the present study, the effect of w/c ratio on IRH and AS of IC concrete was investigated, and a two‐stage prediction model of AS based on the results of IRH for IC concrete considering the effect of w/c ratio was proposed. The experiment results and analysis indicated that IRH of IC concrete increased as increase of w/c ratio, and development of IRH experienced two stages: a water‐vapor saturated stage with 100% RH (stage I), and a gradually reducing stage in which IRH decreased gradually (stage II); critical time of IC concrete increased as increase of w/c ratio; expansion peak of IC concrete increased as increase of w/c ratio; AS and AS rate of IC concrete decreased as increase of w/c ratio; IRH, critical time, and expansion peak of IC concrete were higher than that of ordinary concrete; AS and AS rate of IC concrete were lower than that of ordinary concrete.

Experimental Investigation on Correlation between Autogenous Shrinkage and Internal Relative Humidity of Superabsorbent Polymer–Modified Concrete

This research investigated the effect of superabsorbent polymers (SAPs) (0%, 0.17%, 0.35%, and 0.49% of cement content by weight) on the correlation between autogenous shrinkage (AS) and internal relative humidity (IRH) of high strength concrete under sealing conditions. An integrated device was designed to measure the IRH and AS of concrete simultaneously. Experimental results and analysis indicated that (1) the IRH of the SAP-modified concrete at 28 days and the critical time of the IRH increased as dosages of SAPs increased; (2) the expansion of the SAP-modified concrete at an early age was obvious within the first day, and the expansion peak increased as the dosages of SAPs increased; (3) the AS at 28 days and the AS rate of the SAP-modified concrete decreased as the dosages of SAPs increased; and (4) a prediction model for the AS of SAP-modified concrete was proposed considering concrete relative humidity and the quantity of internal curing water.

Mitigation of autogenous shrinkage of high-strength concrete using rice husk ashes with distinct pore structures

The effect of particle size (50% passing size (D50) of 20 μm, 14 μm and 7 μm) and content (8%, 10% and 12% by mass) of rice husk ash (RHA) on the autogenous shrinkage evolution of high-strength concrete was investigated. RHA samples were selected based on differences in their pore structures, which were investigated by means of nitrogen adsorption isotherms, scanning electron microscopy and absorbency tests. Cement–pozzolan hydration development was studied using isothermal calorimetry. The concretes were subjected to mercury intrusion porosimetry and compressive strength tests. Considering a statistical 22 factorial analysis with a central point, the results showed that D50 and the interaction between D50 and RHA content influenced the autogenous shrinkage at 28 and 100 days. The water absorbed internally by the preserved RHA pore structure (D50 ≈ 20 μm) in the high cement replacement (12% RHA) mixes reduced the final autogenous shrinkage of concrete without a decrease in compressive strength. In addition, the RHA with a more preserved pore structure accelerated the hydration kinetics by heterogeneous nucleation. However, this behaviour did not influence the early autogenous shrinkage results.

Effect of silica fume on the hardened and durability properties of concrete

AbstractThis paper involves the study on the hardened and durability properties of the concrete at two different grades containing silica fume (SF) with various replacement percentages. Investigation on the performance of the SF was performed for M25 and M40 grades concrete with 0, 5, 10, and 15 % replacement levels at 7, 14, 28, and 90 days. The behavior of SF on the autogenous shrinkage of the concrete was studied for both the grades of concrete in the sealed (SC) and unsealed conditions (USC). The workability of the SF concrete was examined at various levels of replacement by the slump cone test. The hardened properties of the SF concrete were investigated through the estimation of compressive strength (CS) and elastic modulus (EM) at 7, 14, 28, and 90 days, respectively. Acid attack was conducted at 28 days and autogenous shrinkage of the SF concrete was investigated using length comparator at 28 day in SC and USC. Results indicate that upon increase in the percentage of SF, the hardened properties of the concrete increases at higher ages of curing and the shrinkage of the concrete tends to increase for both the grades of concrete.

Study of the Superabsorbent Polymer Additive Effectiveness to Reduce the Autogenous Shrinkage of Concrete without Reducing its Strength

Study of the Superabsorbent Polymer Additive Effectiveness to Reduce the Autogenous Shrinkage of Concrete without Reducing its Strength

Mechanical properties and autogenous deformation behavior of early-age concrete containing pre-wetted ceramsite and CaO-based expansive agent

Autogenous shrinkage (AS) of high-strength and high-performance concrete (HSHPC) is large, which easily leads to early-age cracks and then severely deteriorates the concrete durability. CaO-based expansive agent (CEA) is extensively applied to mitigate the AS of HSHPC, but CEA could not fully achieve its expansion efficacy in HSHPC because of its low water to binder ratio and water amount, causing that CEA hydrates incompletely and the concrete contracts sharply and substantially after the initial expansion. Pre-wetted ceramsite (PWC), as an internal curing agent, could decrease effectively the AS of HSHPC. Based on the mechanism of AS reduction of CEA and PWC, the combination use of CEA and PWC could reach a synergistic effect on AS in HSHPC. However, there still lacks a synthetic study on the effects of the compound use of PWC and CEA on the mechanical properties and autogenous deformation of concrete. Thus, this study carried out the experiments on mechanical behaviors and autogenous deformation of concrete with PWC or/and CEA addition. The test results claimed that the PWC addition enhanced the compressive and splitting tensile strength while the opposite results were obtained by CEA addition. In addition, both PWC and CEA addition weakened the dynamic elastic modulus of concrete. Meanwhile, the PWC and CEA incorporation had a significant improving effect on the internal relative humidity in concrete. The AS of concrete was greatly mitigated by PWC addition. The IC water of PWC could improve the expansion efficacy of CEA as well as greatly decrease the contraction at the later stage. A remarkable synergistic mechanism on AS mitigation was observed with the combined use of PWC and CEA, which is significantly beneficial to control the AS-induced cracking.

Application of light-burnt dolomite as a mineral addition in concrete

Growth in the production of cement has led to increasing demands for mineral additions. This study was conducted to develop an alternative addition by calcining dolomite at 800°C to obtain a mixture of periclase (MgO) and calcite (CaCO3). The light-burnt dolomite (LBD) was used to prepare blended cements. The hydration, setting time and microstructure of the cement were assessed and the compressive strength and deformation of concrete made using the LBD cements were measured. The results showed that the blended cement had no unfavourable effects on setting time or hydration. It was also found that the autogenous shrinkage of concrete can be mitigated with a replacement of LBD up to 20% and the free expansion levelled off early and was kept at a low level. The compressive strength of concrete made with the blended cement, especially with 10% LBD, was higher than that of plain concrete, which is partly related to the decrease of porosity, the fineness of pore diameters and interface enhancement due to the interaction of the LBD and the clinker.

Time-zero and deformational characteristics of high performance concrete with and without superabsorbent polymers at early ages

Internal curing with superabsorbent polymers (SAP) can help lower early-age cracking risk of high performance concrete, by reducing both autogenous shrinkage and thermal strain. In this paper, early-age properties of a concrete mixture (with water-to-binder ratio of 0.25) with and without SAP were examined. First, a practical and convenient method for determining time-zero of concrete with and without SAP based on the rate of temperature change induced by cement hydration was proposed. The validity of the proposed method was demonstrated through the good agreement between its determined time-zero values and the corresponding time (i) of divergence between chemical and autogenous shrinkage as well as (ii) when stress due to restrained deformation started to develop. Second, autogenous shrinkage of concrete with different SAP amounts was studied, together with the temperature dependency of autogenous and self-desiccation shrinkage of concrete containing 0.33% SAP. The addition of 0.33% SAP was found to have completely mitigated autogenous shrinkage of early-age concrete. Third, the coefficient of thermal expansion (CTE) of concrete with and without SAP was reliably measured. It is shown that both internal curing (using SAP) and external curing can effectively reduce the CTE, thereby reducing the associated thermal stresses and the risk of thermal cracking. In addition, the inclusion of SAP was found to compromise mechanical properties of concrete during the first 7 days, but such adverse effects became rather small at later ages.

Influence of ground granulated blast furnace slag on the early-age anti-cracking property of internally cured concrete

The influence of ground granulated blast furnace slag (GGBFS) on the mechanical properties and autogenous shrinkage of concrete has been studied. However, investigations on the influence of GGBFS on the early-age anti-cracking property of internally cured high performance concrete (ICC) with super absorbent polymers (SAPs) are still lacking. Investigations on the anti-cracking property of ICC with GGBFS were conducted under adiabatic condition at uniaxial restraint degree by using Temperature Stress Test Machine in the present study. Results and corresponding analysis showed that: (1) the addition of SAPs decreased the autogenous shrinkage, restrained tensile stress rate, and increased the temperature drop, as well as increased the anti-cracking property of high performance concrete; (2) the temperature rise, temperature drop and cracking stress of ICC under adiabatic condition decreased with the increase of GGBFS content; (3) the autogenous shrinkage and restrained tensile stress rate of ICC increased with the increase of GGBFS content; (4) the early-age anti-cracking property of ICC estimated by using integrated criterion decreased with the increase of GGBFS content.

Pozzolanic Reactivity and the Influence of Rice Husk Ash on Early-Age Autogenous Shrinkage of Concrete

In this study, the role of a locally available rice husk ash (RHA) in reducing early-age shrinkage of high performance concrete (HPC) after evaluating its pozzolanic reactivity was evaluated. The X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were performed after burning rice husk to 700 and 950 oC. Presence of relatively high deposits of amorphous siliceous phases in RHA at 700 oC indicated its pozzolanic potential. Subsequently, this RHA was ground to desired fineness, followed by sieving through sieve No. 200. Eventually, the fine RHA was used as a substitute of cement in different percentages (10, 15 and 20%) to evaluate its influence in mitigating autogenous shrinkage in concrete. Prismatic concrete beams (100 mm x 100 mm x 800 mm) were cast to measure autogenous shrinkage along with cylinders (150 mm dia. x 300 mm height) to test compressive strength of concrete. The results indicated a slight increase in compression strength with addition of 10% RHA, which however, reversed and slightly reduced in concretes containing 15 and 20% RHA. Unlike strength results, the trend of autogenous shrinkage was rather uniform as the rate as well as the amount of early-age autogenous shrinkage continued to decrease with increasing percentage of RHA. Moreover, despite of reduced rate during first 24 hours, thereafter, the effect of 20% RHA on further reduction of autogenous shrinkage was insignificant and ended up only slightly lesser than the 15% RHA concrete at 7 days. Finally, the control cement sand mortar and mortar containing 15% RHA were cast to further validate the pozzolanic reactivity of RHA through scanning electron microscopy (SEM), EDX and thermogravimetric analysis (TGA) tests. An observation of reduced amount of calcium hydroxide (Ca(OH)2) in RHA mortar samples indicating its excellent pozzolanic potential when used as a partial substitute of cement in HPC.

Water movement in Internally Cured Concrete

Currently, ordinary cement concrete uses external curing. For high-strength or high-performance concrete, implementing external curing is difficult and inefficient. In these types of concrete, the rather large cement content and low water-binder ratio form very dense cement paste. Thus, not only the autogenous shrinkage of concrete is increased, but the effectiveness of external curing is also reduced. To ensure the quality of the concrete, Internal Curing (IC) has been proposed. With IC, water is generally supplied via internal reservoirs such as saturated lightweight aggregates and superabsorbent polymers. The volume of internal water, which is not part of the volume of the mixing water, cures the concrete from the inside.This paper presents our results of theoretical research and calculations on water movement in internally cured concrete. The efficacy of internal curing depends on parameters such as the volume of internal curing water, the structure of the porous system in lightweight aggregates and cement matrix, curing temperatures. To demonstrate those factors’ dependence on water displacement, we set up a theoretical function through a model that, based on the law of fluid flow and the system’s law of capillary attraction, connects the capillary in lightweight aggregates with the capillary in the cement stone. From the empirical relationship of hydrated thermal of cement and porosity ratio in concrete, we make preliminary calculations of the water movement distance in internally cured and differently aged concrete. These analyses show the feasibility and effects of internal curing.

Effect of cementitious permanent formwork on moisture field of internal-cured concrete under drying

Drying shrinkage of concrete may still be the main source of cracking in concrete structures, even though the autogenous shrinkage of concrete can be effectively reduced by using internal curing. In the present paper, the effect of internal curing with pre-soaked lightweight aggregate and engineered cementitious composite permanent formwork (ECC-PF) on a moisture distribution in three kinds of concrete in a drying environment are investigated from both aspects of experiments and theoretical modeling. The test results show that the combination use of ECC-PF and internal curing can well maintain the humidity at a relatively high level not only at a place far from drying surface, but also at a place close to the drying surfaces. The developed model can well catch the characteristics of the moisture distribution in concrete under drying and the impacts of internal curing and ECC-PF can well be reflected as well. The model can be used for the design of concrete structures with combination use of internal curing and permanent formwork.

Influence of autogenous shrinkage on mass transport properties of concrete

Autogenous shrinkage in concrete is defined as the change of volume after initial setting occurs. It develops at very early ages as a result of chemical shrinkage and self-desiccation effect. These produce significant microcracks in high-strength concrete allowing the entrance of aggressive agents such as carbon dioxide, chlorides, and sulphates which cause concrete deterioration. Although considerable research of autogenous shrinkage has been done, uncertainty remains concerning the influence in concrete durability. Therefore, the purpose of this study was to quantify and analyse the effect of autogenous shrinkage on the mass transport properties of concrete using three transport tests: oxygen diffusion, oxygen permeation, and water absorption. Two methods, for three different binders, were first carried out to determine a control mixture that produces the least autogenous shrinkage: adding SRA and curing in a fog room. Subsequently, transport test results between the selected control mixture and mixtures highly affected by autogenous shrinkage were compared for different binders. Results revealed that specimens with SRA presented the least autogenous shrinkage; therefore, it is suggested to be considered as control samples. It was also found that autogenous shrinkage significantly affects the transport coefficients in concrete made with secondary cementitious materials which from a serviceability point of view could reduce the life span for any structure made with high-strength concrete. This investigation also confirmed that most of the autogenous deformation occurs during the first two weeks after casting therefore enough care should be taken when curing.

Autogenous Shrinkage and Expansion Related to Compressive Strength and Concrete Composition

An extensive research was undertaken in order to determine the dependence of shrinkage of high and normal strength concrete on the compressive strength and concrete composition. The part of research concerning dependence of autogenous shrinkage on compressive strength is presented in this paper. Ten groups of concrete, with the total of twenty nine mixtures, were prepared. Concrete mixtures of each individual group were made using the same quantity of water, while the quantity of cement (CEM II/A-S 42, 5R) and mineral admixture (silica fume) was varied in each group. Concrete groups differed according to the quantity of water. Autogenous shrinkage of concrete was monitored together with the influence of initial curing in water on concrete shrinkage. Initial autogenous expansion was noticed during testing autogenous shrinkage, especially on normal strength concrete. Based on the analysis of experimental results, the dependence of autogenous shrinkage at one day of concrete age on compressive strength was defined. The dependence of autogenous shrinkage at later ages on compressive strength of concrete was also presented. Finally, the autogenous shrinkage components of best-known theoretical shrinkage prediction models were compared with experimental data.

Autogenous Shrinkage Reduction with Untreated Coal Bottom Ash for High-Strength Concrete

The effect of untreated bottom ash on autogenous shrinkage reduction for high-strength concrete was investigated. A type of commercialized artificial lightweight aggregate was used as a reference material to compare the efficiency of internal curing by bottom ash. A type of commercialized artificial lightweight aggregate- expanded shale-was used as a reference material to evaluate the efficiency of internal curing with bottom ash. Prior to evaluating the shrinkage of concrete, absorption/desorption properties and water transfer characteristics of both materials were measured. The deformations of the concrete with both materials were measured under sealed and unsealed conditions. In addition, the mass loss of concrete by drying was measured. It was found that the autogenous shrinkage of concrete was decreased or eliminated by the use of bottom ash aggregates. However, the efficiency of the bottom ash with respect to shrinkage reduction was less than the expanded shale. © 2016, American Concrete.

Mesocosmic study on autogenous shrinkage of concrete with consideration of effects of temperature and humidity

A study on the autogenous shrinkage (AS) of concrete from a mesocosmic perspective was carried out using numerical simulation technology. The temperature history and the autogenous relative humidity (ARH), two factors that have been shown to have occasional influence on this process in previous studies, were introduced into this study. According to these concepts, a program for simulation of the temperature field, humidity field, and stress field based on the equivalent age method and a fully automatic aggregate modeling tool were used. With the help of these programs, the study of a small concrete specimen provided some useful conclusions: the aggregate and the matrix show distinct distribution properties in the temperature field, humidity field, and stress field; the aggregate-matrix interface has a high possibility of becoming the location of the initial cracking caused by AS of concrete; the distribution of random aggregates is extremely important for mesoscopical analysis; and the temperature history is the main factor affecting the AS of concrete. On the whole, inherent mechanisms and cracking mechanisms of AS of concrete can be explained more reasonably and realistically only by considering the different characteristics of material phases and the effects of temperature and humidity.