Autogenous Volume Deformation Research Articles

Effect of Different Fineness of Cement on the Autogenous Shrinkage of Mass Concrete under Variable Temperature Conditions

The internal temperature of the mass concrete is not constant. In the actual project, the internal temperature of the concrete will experience a process of rapid warming to reach the peak temperature and then slow down. In this study, volume measurement method is used to simulate the internal volume deformation of mass concrete under actual engineering conditions. The embedded strain gauge was embedded in concrete with a water-cement ratio of 0.32 for 28 days, and the development of total volume deformation and autogenous volume deformation of concrete under variable temperature conditions was studied by external heating of concrete. The results show that the finer the cement, the earlier the concrete starts to shrink, and the greater the total shrinkage of the concrete. The high temperature will promote the hydration of cement with different fineness and will reduce the total porosity of their paste, but the proportion of harmful pores in the paste with finer cement particles is lower.

Application of magnesium oxide expansive agent in hydraulic concrete in China

This paper reviews and summarises the use of magnesium oxide (MgO) in hydraulic concrete in the following projects in China: Baishan hydropower station unexpectedly discovered the beneficial effects of MgO; Dongfeng hydropower station actively used MgO as an expansive agent for the first time in the main project; Changshaba hydropower station used MgO expansive agent for the first time in a full arch dam; Huangjiazhai hydropower station broke through 6% of MgO content for the first time in normal state concrete; and Dahe reservoir broke through 6% of MgO content for the first time in roller-compacted concrete. Findings indicate that the production process, transportation equipment, pouring process, burying of observation instrument, and so on, for concrete mixed with MgO are exactly the same as concrete without MgO. The long-term autogenous volume deformation of MgO concrete presents a good delayed micro-expansion discipline, which matches the long temperature drop process of dam concrete. The use of MgO expansive agent in dam concrete improves concrete's anti-cracking ability, simplifies temperature control measures of dam concrete, speeds up construction progress and saves project investment. At the same time, this paper points out the appropriate quality standards for the MgO expansive agent used in dam concrete and its soundness content that shall not be exceeded.

Influence of Specimen Size on Autogenous Volume Deformation of Long-Aged MgO-Admixed Concrete

The transformation law of autogenous volume deformation of MgO-admixed concrete with specimen size was revealed through continuous observation on standard-size (Φ200 mm × 500 mm), medium-size (Φ250 mm × 500 mm), and large-size specimens (Φ250 mm × 600 mm) over 6 years. Besides, the pore parameters of concrete core samples obtained from autogenous volume deformation specimens in the 1st, 3rd, and 6th years of age were investigated. The results show that the autogenous volume deformation of MgO-admixed concrete increases with the increase in the MgO content or age. The expansion rate of the concrete specimen decreases after the age of 360 days, and the autogenous volume expansion deformation of the specimen tends to be stable after about 2 years. When the size of the specimen changes, the autogenous volume deformation of MgO-admixed concrete decreases with the increase of specimen size. During the age of 2–6 years, the expansion of medium- and large-size specimens is reduced by 6–10 and 15–20%, respectively, compared with the standard-size specimens under the same MgO content. With the condition of an appropriate MgO content, regardless of the size of the specimen, the pore structure of the concrete becomes better and better with the growth of age, the concrete becomes denser and denser, and the expansion caused by MgO hydration will not cause damage to concrete structures.

Experimental study on autogenous volume deformation of RCC mixed with MgO

The application of MgO to control thermal stress for concrete structures has achieved many accomplishments over the years. MgO is an important type of materials for the shrinkage cracking control of mass concrete in general, and Roller Compacted Concrete (RCC) dams in particular. Previous studies have investigated the application of MgO concrete and have proven the cracking prevention of MgO concrete. The purpose of this paper is to measure the Autogenous Volume Deformation (AVD) of RCC mixed with the MgO-expansive agent. And these experiments were conducted under different MgO content, temperature and curing time conditions. The experimental results of the AVD process show that the AVD process increased with the MgO content, curing time and temperature condition. The reseach outcomes are evidence that the hydration of expanded materials in concrete can compensate for shrinkage.

Modeling of autogenous volume deformation process of RCC mixed with MgO based on concrete expansion experiment

Abstract To improve concrete crack prevention performance for high concrete dams, several studies have shown that the addition of MgO-type expansive can compensate for shrinkage of concrete and prevent concrete from cracking. In this paper, the Autogenous Volume Deformation (AVD) process of MgO concrete as a function of curing age, temperature and MgO content has been presented. The objective of this paper is to develop a hyperbolic expansive model, in which the parameters are developed and validated for the modeling of AVD process of MgO concrete and compared with Shu-hua Liu’s method. In addition, the correction coefficients have been proposed and the relationships between the model parameters and MgO content have been also introduced. The model parameters were obtained based on the experimental data under laboratory conditions for the AVD process. Then the final equation of the hyperbolic expansive model is determined by the MgO content, the curing temperature and time. The calculation results are then compared with the measured data; and the reasonably good correlation between simulated and measured results indicates that the selected values of Gpre, c(T), and the relationships between model coefficients, MgO content, and temperature, are almost perfect. It will enhance the design reliability of the Linxihe RCC arch dam project and others.

Effect of expansive agent and internal curing agent on crack resistance of C50 silica fume wet-mix shotcrete

High-strength shotcrete is always needed to strengthen rock support. However, it will reversely increase the crack risk. Crack normally goes against the durability and shortens the service life of shotcrete. The objective of this article was to improve the crack resistance of shotcrete with expansive agent and internal curing agent. C50 shotcrete with 10% of silica fume was taken as reference mix composition. Ring test and thermal stress test simulating actual temperature, relative humidity, and constraint were carried out to directly assess crack resistance. Restrained deformation, autogenous volume deformation, and pore structure were measured to study how expansive agent and internal curing agent resisted crack. The results indicated that 4% of expansive agent was enough to improve crack resistance of C50 shotcrete. It could fill internal pores and produce compressive pre-stress at earlier age which could be used to compensate shrinkage at later age. Furthermore, the crack resistance of C50 shotcrete could be further promoted when internal curing agent was employed together with expansive agent. The internal curing agent was able to reduce auto-shrinkage by decreasing the loss of internal relative humidity. In addition, it could also enhance the hydration degree of expansive agent, which would strengthen the role of expansive agent on resisting crack.

Studies on the wet expansion deformation of hydraulic concrete with fly ash under non-standard temperatures

Concrete manifests wet expansion deformation when the moisture content of concrete increases via the seeping of water into the pores of the concrete. Moreover, concrete manifests different wet expansion deformations if the hydraulic concrete is submerged in water under different temperature histories. In the present work, wet expansion tests are conducted using hydraulic concrete (in which a strain gauge is embedded) cured under different temperatures. First, the statistical model of the measured strain is established before the concrete is submerged in water, and then the coefficient of thermal expansion and the autogenous volume deformation of the concrete are obtained. The wet expansion deformation of the concrete is then separated according to the measured strain after the concrete has been submerged in water. The analysis results show that the stability values of wet expansion deformation of the 3 groups of concrete specimens under different temperature histories are 35.57 μe, 42.35 με and 31.07 με. If the relationship between the wet expansion deformation of concrete and the moisture content of concrete is assumed to be linear, then the aforementioned stability values are equivalent to increases in the concrete moisture content of 1.052%, 1.253% and 0.919%, respectively. In addition, the wet expansion deformations of concrete specimens are positively correlated with the average temperature during the test process.

Cracking propagation of hardening concrete based on the extended finite element method

Self-deformation cracking is the cracking caused by thermal deformation, autogenous volume deformation or shrinkage deformation. In this paper, an extended finite element calculation method was deduced for concrete crack propagation under a constant hydration and hardening condition during the construction period, and a corresponding programming code was developed. The experimental investigation shows that initial crack propagation caused by self-deformation loads can be analyzed by this program. This improved algorithm was a preliminary application of the XFEM to the problem of the concrete self-deformation cracking during the hydration and hardening period. However, room for improvement exists for this algorithm in terms of matching calculation programs with mass concrete temperature fields containing cooling pipes and the influence of creep or damage on crack propagation.

Factors analysis on autogenous volume deformation of MgO concrete and early thermal cracking evaluation

Micro expansive MgO concrete was produced by batching conventional raw materials and expansion agent light-burnt MgO obtained by magnesite decomposition through rotary kiln. Many factors, including calcinations condition, batching method as well as variations in raw materials had been investigated. Results indicated that MgO agent tailored to shrinkage-compensating hydraulic concrete was obtainable by adjusting calcinations condition and uniform distribution of MgO in concrete was gainable by premixing MgO agent with other cementitious materials for 20min and fed in the mixer all at once. Autogenous volume deformation of MgO concrete with reaction time ranging between 50s and 200s tended to stabilize after approximate two years development with no retraction or drop-back, and it exhibited good relationship with long-term water absorption of aggregates while alternative method to accurately quantify the effective periclase in clinker should be explored. Concrete with incorporation of 4% MgO agent with reaction time of 100s was ranked the best in thermal cracking resistance and this solution was adopted for diversion tunnel sealing off in Xiluodu, Xiangjiaba and Baihetan hydropower stations.

Influence of specimen size on autogenous volume deformation of concrete with magnesium oxide

In order to investigate the influence of specimen size on autogenous volume deformation of concrete with magnesium oxide (MgO), the role of autogenous volume deformation of MgO concrete was tested. The results show that the specimen size has an obvious influence on autogenous volume deformation of MgO concrete.

Interventions of Retarders on the Hydration Process of CaO Expansion Clinker

The volume deformation test, differential scanning calorimetry and chemical titration technique were used to experimentally research the interventions of retarders on the free autogenous volume deformation of cement paste doped with CaO expansion clinker at different ages systematically, as well as the hydration rate and hydration process of CaO expansion clinker. Two types of retarders were used as following: sodium gluconate and sodium citrate. The experimental results show that the two retarders can delay the hydration process of CaO expansion clinker, slow down its hydration rate both in pure water and cement paste. At the same time, the free autogenous volume deformation of cement paste was increased. In this sense, the use of retarders is favorable to improve the expansion efficiency of CaO expansion clinker.

Early age cracking behavior of internally cured mortar restrained by dual rings with different thickness

This paper presents the results of research which examined the early age cracking behavior of internally cured and plain mortars under restraint. Residual stress development, cracking stress and age of internally cured and plain mortars restrained by dual rings with different thickness were studied in detail. Tensile stress resistance was calculated according to the results of fracture test. Autogenous volume deformation was tested also. The obtained results reveal that, internally cured and plain mortars are unlike to crack at first 2days due to the low residual stress. After that age, residual stress in plain mortar goes up quickly and induces the damage of material, which implies the higher possibility to crack with the past of age. Compared to plain mortar, lower shrinkage or expansion, lower elastic modulus and less damage are advantages of internally cured mortar to diminish the risk of cracking.

Allowable Height Difference between Adjacent Monoliths with Spherical Surface Key Groove in Transverse Joints

The calculation method of the minimum aperture of transverse joints with spherical surface key groove was introduced in this study. Based on the computation theory of allowable height difference between adjacent monoliths proposed by Bofang Zhu, the analytical model of allowable height difference of Xiluodu arch dam was established with consideration of the effect of main factors on the transverse joints deformation, including the temperature, autogenous volume deformation, self-weight and foundation. After the horizontal and vertical deformations of transverse joints was required, according to the form of spherical surface key groove, the aperture of each part of key groove and the minimum aperture were obtained at several height difference between adjacent monoliths. The allowable height difference was determined on the condition of meeting the grouting requirements of transverse joints. The result shows that the allowable height difference for Xiluodu arch dam should not be more than 30m.

Autogenous Volume Deformation of Concrete due to MgO under the Temperature History of a Diversion Tunnel Concrete

Using MgO type expansive agent is considered as a convenient and effective method to reduce cracks in dam concrete, but the research on autogenous volume deformation of concrete with MgO type expansive agent under the temperature history of real structure is still unclear. In this paper, the temperature history of a diversion tunnel concrete was selected to discuss the autogenous volume deformation of concrete with different activities and dosages of MgO type expansive. The results showed that the autogenous volume expansion of concrete with MgO type expansive agent increased with the content and the activity of MgO type expansive agent. The expansion values of concrete with the content of 4%, 5% and 6% MgO type expansive agent are 51×10-6, 85×10-6 and 105×10-6 in temperature rise stage, and 43×10-6, 56×10-6 and 71×10-6 in temperature decrease stage. The expansion values of concrete with the activity 31s, 138s and 240s MgO type expansive agent are 36×10-6, 51×10-6 and 66×10-6 in temperature rise stage, and 32×10-6, 43×10-6 and 62×10-6 in temperature decrease stage. After 150d the autogenous volume deformation due to MgO type expansive agent did not increase any more.

Autogenous Volume Deformation and Creep Properties Analysis of C60 High Performance Concrete and C60 High Strength Concrete

Based on engineering practice, autogenous volume deformation and creep properties of C60 high performance concrete(C60 HPC) and C60 high strength concrete(C60 HSC) were evaluated in the study. The results showed that the cement partly-replaced with fly ash could significantly decrease the creep deformation, creep coefficient and creep degree. In comparison with C60 HSC, the creep coefficient and creep degree of C60 HPC were decreased 17.9％and15.8％ in 28 days, 22.9% and 21.0% in 270 days. For C60 HPC and C60 HSC at the same age, autogenous volume deformation of C60 HPC is greater than that of C60 HSC, but they were both less than 80×10-6 , and the autogenous volume deformation was basically completed in 7 days.

Research on autogenous volume deformation of concrete with MgO

The autogenous volume deformations of concrete with MgO expansive materials and fly ash cured in different ages were measured, and the morphologies of it were observed through scanning electron microscope. The results showed that the autogenous volume deformation of the concrete increased with the curing ages and the content of MgO expansive materials. The expansions of concrete with MgO became less in later ages and unlimited expansion did not appear. Fly ash may inhibit the autogenous volume expansion of concrete with MgO expansive materials, and the effect became more significant with the dosage increase of fly ash. The micro-expansion caused by the additive MgO expansive materials filled the pores of paste and made the structure denser, and might compensate the shrinkage of concrete, decrease the cracking of concrete works and improve the durability of concrete.

Influence of Crushed Basalt Aggregate on Crack Resistance of Concrete

The crack resistance of concrete with crushed basalt aggregate was studied. Compared with the limestone concrete, the basalt concrete has larger drying shrinkage and autogenous volume deformation. The linear expansion coefficient of basalt concrete is 1.3×10－6 /°C larger than that of limestone concrete, and it has additional temperature deformation of 24.1×10－6. According to the analysis on temperature-stress of concrete, the cracking temperature of basalt concrete is 8.9°C higher than that of limestone concrete, and the crack resistance of basalt concrete is unfavorable.

Research on Concrete Temperature Control and Crack Prevention for Pumping Station Complicated Structure

The water passageway structure of pumping station is both mass concrete structure and complicated structure. Cracks always appear in these areas during construction period. It will shorten the building life, and endanger the safety of pumping station. Three dimensional finite element method is adopted to simulate the temperature field and stress field of pump station in construction. The considering loads include gravity, temperature, autogenous volume deformation, and creep. The temperature and the first principle stress duration curves of easily cracking area are analyzed in different cases. After optimization of different temperature control measure, the tensile stress of different areas in early age or later age can be controlled lower than tension strength, and the cracking prevention safety factor can be raised. It is found that pipe cooling, surface insulation, pouring intermission, structure constrains can change the tensile stress obviously for pumping station. The influence of these factors is separately concluded.

Stress Field Simulation of Concrete Structure Considering Influence of Temperature on Autogenous Volume Deformation

Aotugenous volume deformation is one of the influence factors of stress field of concrete structure. Generally, the influence of temperature on autogenous volume strain is not considered in calculation. In fact, the difference of internal and surface temperature of concrete structure can lead to different hydration reaction and different autogeneous volume deformation. In order to find out the effect of temperature difference on aotogenous volume deformation and stress field of concrete structure, a model is established and a corresponding example is given. The result shows that it is necessary to take temperature effect into consideration while calculate autogenous volume deformation in stress field simulation of concrete structure.

Autogenous Volume Deformation of Hydraulic Concrete

In hydraulic mass concrete construction, the autogenous volume deformation is a more important factor for concrete to generate adverse tensile stress, which will lead to structural cracks. The adverse effect of autogenous volume deformation of concrete will be offset by cooling pipe skills. That is, to make the volume deformation unchangeable or minimum after pouring, the autogenous volume deformation is set to be counteracted by moderate temperature expansion deformation. The simulation results show that the adverse effect of autogenous volume shrinkage deformation of concrete can decrease obviously by controlling cooling water during construction period. The results can provide certain references to hydraulic mass concrete rapid construction.