Measurement Of Autogenous Shrinkage Research Articles

Assessment of determination methods for time-zero of autogenous shrinkage in cement mortars

Assessment of determination methods for time-zero of autogenous shrinkage in cement mortars

Utilizing porcelain tile polishing residue in eco-efficient high-strength geopolymers with steel microfibers

Utilizing porcelain tile polishing residue in eco-efficient high-strength geopolymers with steel microfibers

Substitutive effect of nano-SiO2 for silica fume in ultra-high-performance concrete on fiber pull-out behavior

This study investigated the effect of substituting nano-SiO2 for silica fume on the fiber-matrix interfacial bond performance of ultra-high-performance concrete (UHPC). In this study, silica fume was substituted by nano-SiO2 in the weight range of 0–50%. The degree of pozzolanic reaction of binder materials was evaluated using the thermogravimetric analysis (TGA) and compressive strength measurement. The single fiber pull-out test was conducted along with a measurement of autogenous shrinkage to evaluate the interfacial bond. The degree of pozzolanic reaction of nano-SiO2 was found to be higher than that of other binder materials. Although the packing density was predicted to increase continuously up to a substitution ratio of 50%, the highest compressive strength was obtained when 10% of silica fume was replaced by nano-SiO2, which improved the compressive strength by 5.9% compared to that of the plain sample. The autogenous shrinkage increased with an increasing content of nano-SiO2 up to 30%; however, it remained similar beyond the nano-SiO2 content of 30%. The best pull-out performance was obtained when 20% of silica fume was replaced by nano-SiO2, in which the average bond strength and pull-out energy were improved by approximately 21 and 68%, respectively. Therefore, substitution of 10–20% of silica fume by nano-SiO2 was recommended as an optimal amount considering the improvements of the compressive strength and fiber-matrix bond performance of UHPC.

Modifications in hydration kinetics and characteristics of calcium aluminate cement upon blending with calcium sulfoaluminate cement

The present study explores the modifications in hydration kinetics and characteristics of calcium aluminate cement (CAC) upon blending with calcium sulfoaluminate (CSA) cement. CAC was replaced with CSA cement at 0, 30, 50, 70, or 100 wt%. The hydration properties of the samples were evaluated and characterized by X-ray diffraction, thermogravimetric analysis, 27Al nuclear magnetic resonance spectroscopy, compressive strength tests, isothermal calorimetry, autogenous shrinkage measurements, and thermodynamic modeling. The test results indicated that the incorporation of CSA cement altered the hydration pathway of the CAC clinkers, promoting the formation of AFm phases over katoite. In addition, the addition of CSA cement increased the compressive strength development and reduced the total hydration heat release. In contrast, the occurrence of heat release rate peak was advanced by the addition of CSA cement. Furthermore, the CSA cement compensated for the autogenous shrinkage development of the samples, reaching almost no volumetric movement in the sample with 50% CSA cement.

Internal curing of cement pastes by means of superabsorbent polymers visualized by neutron tomography

Superabsorbent polymers (SAPs) are used to counteract self-desiccation in order to mitigate autogenous shrinkage, a problem in cementitious systems with a low water-to-cement ratio. The release kinetics during internal curing are of importance as not all SAP types are able to efficiently mitigate autogenous shrinkage. In this study, neutron tomography is used to study and visualize the water release kinetics over time. Per-voxel analysis of the time-attenuation curve was performed using piecewise-constant functions. Two different SAP types were studied, one being able to mitigate autogenous shrinkage and one quickly releasing its stored water after final setting. The tomography results correspond to autogenous shrinkage measurements and nuclear magnetic resonance tests. The visualization provides information on the time of water release by the SAPs after setting and the time window of internal curing. This opens additional insights towards the application of SAPs in the construction sector and provides information on the mechanism of internal curing. • The kinetics of water release from SAPs were studied by neutron tomography. • The time window for internal curing was linked to the water release from SAPs. • The water release links to the SAP effectiveness to mitigate autogenous shrinkage. • One SAP type was effective while another prematurely released its stored water.

Deformation of Alkali-Activated Materials at an Early Age Under Different Curing Conditions.

The production of alkali-activated materials (AAMs) is known for its environmentally friendly processing method, where several amorphous-rich aluminosilicate material sources combine with an alkali media solution to form solid, ceramic-like materials. In terms of the Si:Al, Na(K):Al, and Na(K):H2O ratios, the theory of AAM formation is quite well developed, but some open questions in the technology process remain, especially with regards to the means of curing, where the generation of defects can be persistent. Knowing that deformation is extremely high in the early ages, this study investigates the effects of temperature and moisture on shrinkage behavior within the first 72 h of AA pastes made from ladle (LS) and electric arc furnace (EAF) slag and activated by sodium silicate (Na2SiO3). The method to determine the deformation of alkali-activated slag-based materials, in terms of both autogenous and drying shrinkage, was based on the modified ASTM C1698-19 standard for the measurement of autogenous shrinkage in cement pastes. Autogenous deformation and strain were measured in four samples, using the standard procedure at room temperature, 40 and 60°C. Furthermore, using an adjusted method, nine samples were characterized for strain and partial surface pressure, while drying at room temperature, 40, or 60°C at a relative humidity of 30 or 90%. The results show that the highest rate of autogenous shrinkage occurred at a temperature of 60°C, followed by drying shrinkage at 60°C and 30% relative humidity, owing to the fact that the rate of evaporation was highest at this moisture content. The study aimed to provide guidance regarding selection of the optimal curing set in order to minimize deformations in slag-based alkali-activated materials. In the present case, curing at a temperature of around 40°C under lower moisture conditions for the first 24 h provided optimal mechanical properties for the slags investigated. The methodology might also be of use for other aluminosilicate sources such as metakaolin, fly ash, and mineral wool–based alkali-activated materials.

Comparison of autogenous shrinkage measurements by different methods in case of fast-hardening mortar

Autogenous shrinkage in the volume of cementitious materials results from changes in the microstructure and environmental conditions. These deformations can be sufficient to cause premature cracking of structures, especially the fast hardening materials or thin products with large exchange surfaces, such as paving, screeds and cement-glass composite. The appearance of cracks influences the quality and aesthetics of the works. The dimensional variations can be observed immediately after the cement and the water have been brought into contact during mixing. In this research, the endogenous shrinkages of a fast hardening mortar based on ettringite binder were studied with different methods. In this mortar, there is not only the shrinkage phenomenon but also the swelling relating to the early ettringite formation. Therefore, the understanding of the dimensional variation with different measurement methods is very important. The results indicate that the endogenous shrinkage measured by linear methods and volumetric methods are in good agreement. All measurement method well recorded both a quick shrinkage and a swelling phenomenon in the mortar.

Autogenous-shrinkage model for concrete with coarse and fine recycled aggregate

Autogenous shrinkage of recycled-aggregate concrete (RAC) is important for design of concrete structures with recycled aggregate, however, there are few studies on this critical topic. To address this, an experimental research study was undertaken to investigate the autogenous shrinkage of RAC made with fine and coarse recycled aggregate (termed FRA and CRA, respectively) to support the modification of existing shrinkage models to account for the effects of these aggregates. The experimental study investigated replacement ratios of 0%, 50% and 100% of one type of CRA and two types of FRAs; 15 mix designs were considered in total. Measurement of autogenous shrinkage was conducted on 30 specimens (two specimens for each mix design) for 360 days. Test results showed: (1) both FRA and CRA significantly reduced the autogenous shrinkage of RAC and (2) the influence of FRA is more significant with increasing content of CRA, and vice versa. Based on these results, a modified autogenous-shrinkage model for RAC was proposed, which accounts for the reduced aggregate stiffness and the additional water induced by CRA and FRA. The model provides an accurate prediction of the autogenous shrinkage of RAC.

Experimental study on autogenous shrinkage behaviors of different Portland blast furnace slag cements

Abstract In this study, the differences in autogenous shrinkage behaviors among the Portland blast furnace slag (BFS) cements were investigated experimentally. Portland BFS cements that contain 40–45% BFS were collected from eight different plants in Japan and their autogenous shrinkage at early ages were measured with mortar specimens. After the proper thermal dilation correction of the experimental results, it is indicated that several Portland BFS cements could exhibit significantly different autogenous shrinkage behaviors, even if they are in the same class for the products. The laser diffraction test was conducted to compare fineness of cement particles, but the fineness property of Portland BFS cements was inconsistent with the measured autogenous shrinkages. Subsequently, the chemical composition of each powder and the reaction progress of cement paste specimens were measured by thermal gravimetric analysis and X-ray diffraction Rietveld analysis (XRD). It was realized that the crystallized slag mineral contents through the heat treatment process are consistent with the autogenous shrinkage measurement results and well correlated with hydration level of slag. The crystallized slag mineral contents through the heating process can be an indicator to assess the degree of autogenous shrinkage. The differences in the composition of BFS can be identified through the heat treatment process and this can result in different reaction progresses and autogenous shrinkage behaviors among Portland BFS cements.

Effects of combined expansive agents and supplementary cementitious materials on the mechanical properties, shrinkage and chloride penetration of self-compacting concrete

Abstract In this study, the effects of incorporating expansive agent on the early-age mechanical properties, shrinkage characteristics and durability tests of self-compacting concrete (SCC) with different supplementary cementitious materials (SCMs) are investigated. Fly ash (FA), blast furnace slag (BFS) and metakaolin (MK) are added as partial replacement for cement respectively, while three different kinds of expansive agents are introduced in SCC at 15 wt%, 5 wt% and 1 wt% by cement weight. Results show that SCC presents a slightly lower compressive strength and modulus of elasticity compared to those of reference specimens at early ages, while the pozzolanic reactivity of SCMs lead to an increase the mechanical properties in the long-term strength development. The incorporation of combined magnesia expansive agent and liquid expansion agent indicates a significant reduction in the measurement of autogenous shrinkage and drying shrinkage. Additionally, the chloride ion penetration resistance of SCC is enhanced. Moreover, the combination of magnesia and liquid expansion agents refines pore structure and induces compensation for the auto-desiccation which results in high efficiency in the shrinkage reduction.

Comparison of non-contact autogenous shrinkage measurements and the stress ratio of capillary stress to compressive strength

Abstract The measurement of autogenous shrinkage is a very important and fundamental step before conducting any autogenous shrinkage related research. This study investigates two non-contact autogenous measurement methods using eddy current sensor: non-contact corrugated tube method (CTM) and non-contact vertical prism method (VPM). Comparisons are made between them in terms of starting time, restraint condition, experimental operation and experimental results. In CTM measurement, the effective autogenous shrinkage is defined as the stage after the expansion stage. The corrugated tube would have a restraint effect on free deformation of cement paste inside if the axial stiffness of tube is not small enough compared to its radial stiffness. As for VPM, experimental operations are much simpler and no size effect is found so that effective studies among specimens with different sizes are allowed in this method. Meanwhile, the calculation of capillary stress is introduced and a power function correlation between capillary stress and autogenous shrinkage is found. The stress ratio ( SR ) of capillary stress to compressive strength is firstly proposed to analyze the tendency of autogenous shrinkage. Cement paste with lower W/C has a greater stress ratio. The evolution of SR reflects the competition between the growth of self-desiccation induced stress and the growth of pore structure strength gain.

Comparative shrinkage behavior of ultra-high-performance fiber-reinforced concrete under ambient and heat curing conditions

This study aims to investigate the effect of curing conditions on the free shrinkage behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). For this study, a number of exposed and sealed prismatic UHPFRC samples for drying and autogenous shrinkage measurements were fabricated and tested using two different types of embedded strain gauges. Several other tests, including mechanical tests, X-ray diffraction (XRD), and mercury intrusion porosimetry analyses, were also performed. Test results indicate that steam curing with heat (90 °C, referred to as heat curing) was effective to improve the mechanical properties of UHPFRC at an early age in terms of strength, elastic modulus, and fracture energy absorption capacity. The larger quantities of C-S-H and much smaller total cumulative pore volume were obtained for the steam-cured specimens, compared to those for the ambient-cured specimens. The ultimate autogenous shrinkage of UHPFRC was insignificantly affected by the curing conditions, whereas heat curing accelerated the shrinkage development as compared to ambient curing. In particular, there was no increase of shrinkage strains for UHPFRC after heat curing was finished. The ultimate drying and autogenous shrinkage of UHPFRC were found to be approximately −45 με and −450 με, respectively. Based on literature review, an optimized model was suggested, and the autogenous shrinkage developments of UHPFRC at both ambient and heat curing conditions were successfully predicted based on the equivalent age method.

Examining the “time-zero” of autogenous shrinkage in high/ultra-high performance cement pastes

Abstract The term “Time-zero”, i.e., the time for the start of autogenous shrinkage measurement, is usually used for estimating the cracking potential of structural components. Accurate determination of the “time-zero” is therefore critical for autogenous shrinkage measurement, which is the main objective of this study. There is a general agreement about the existence of a relationship between autogenous shrinkage and RH changes in hardening cement paste. An improved hygrometer method was developed for monitoring the change of internal RH in cement pastes 1 h after casting. This provides immediate experimental results of RH change for determining the “time-zero”. It indicates that the internal RH of cement pastes does not decrease immediately after the final setting time. A new “time-zero” is defined as the onset of internal RH drop, which is more reasonable for estimating the cracking potential of cement-based materials, compared to the “time-zero” represented by the final setting time.

Corrugated tube protocol for autogenous shrinkage measurements: review and statistical assessment

Among different methods of measuring early age autogenous deformation of cementitious materials, the corrugated tube method described in the ASTMC1698-09 standard is one of the most commonly used. Despite the standardization and the common application of this method in the research community, only limited information has been published about the method’s precision. This paper is dedicated to a review of this method, together with a statistical assessment of the results of an experimental study on three cement pastes. The autogenous deformation of cement pastes of water-to-cement ratio 0.30–0.36, with and without internal curing, was measured by different operators in a single laboratory following the standard ASTM procedure. In addition to determining the method’s precision, key factors influencing the results (i.e., rotation, temperature, time-zero) were identified and their effects were quantified. It was found that the method is sensitive enough to resolve different levels of shrinkage and its evolution in time, and that the effect of the operator is not significant. However, considerably high scatter was found between replicate samples within a single operator. The major source of the scatter was due to the inaccuracies in the initial measurement after setting (time-zero), being the reference point for strain determination.

Improvement of autogenous shrinkage measurement for cement paste at very early age: Corrugated tube method using non-contact sensors

Abstract Test methods for the measurement of autogenous shrinkage of cement paste were reviewed, and it is found that few methods can precisely determine the autogenous shrinkage of cement paste at very early age. Therefore, the corrugated tube method was improved by using non-contact linear variable differential transformer (LVDT) sensor for measuring the autogenous shrinkage of cement paste at very early age. The experimental results show that the transformation ratio of the volume deformation to length change for the designed non-contact system can be as high as 0.97, which gives a significant improvement compared to that for the contact system (0.87). Compared to the contact system, the designed non-contact system also has an improved repeatability: the typical standard deviations reach about 50 μm/m and 10 μm/m before and after setting, respectively.

Influence of CaO-Based Expansive Agent on the Deformation Behavior of High Performance Concrete

In order to improve the volume stability of high performance concrete, the effects of deformation behavior of high performance concrete containing CaO-based expansive agent were investigated. Concrete samples prepared without or with CaO-based expansive agent were compared through expansion under water curing at 20°C, drying shrinkage and autogenous shrinkage measurements. According to the experimental and analytical results, the new type expansive agent can control volume stability for high performance concrete. The addition of 10% CaO-based expansive agent not only built effective expansion in high performance concrete whatever under saturated condition or under sealed condition, but also substantially reduced its drying shrinkage.

A review on testing methods for autogenous shrinkage measurement of cement-based materials

Autogenous shrinkage is an important factor for cracking of cement-based materials at early ages. This review summarizes different definitions and testing methods for autogenous shrinkage in literature. Autogenous shrinkage should be defined as the sum of chemical shrinkage and self-desiccation shrinkage. All testing methods in the literature can be divided into two categories: direct and indirect testing methods. Direct testing methods usually measure volumetric or linear dimensional changes. Indirect methods usually measure porosity or change in relative humidity of cement-based materials, which can reflect the change in autogenous shrinkage. Indirect methods need to establish correlations between autogenous shrinkage and porosity or relative humidity.

Early age setting, shrinkage and tensile characteristics of ultra high performance fiber reinforced concrete

Abstract Recently, ultra high performance fiber reinforced concrete (UHPFRC) with compressive strength over 180 MPa and tensile strength of 10 MPa has been developed. Since UHPFRC not only has superior strength, ductility and durability but also reduces the self weight of structures by decreasing the cross sectional areas needed, as such the research for applying UHPFRC to structural members is being widely performed. However, UHPFRC shows different material behavior to normal concrete and conventional high performance concrete. For example, it displays high early age autogenous shrinkage as well as rapid surface drying and surface cracking because of its low water–binder ratio and addition of high fineness admixtures. In this study, therefore, to precisely evaluate the basic material properties of UHPFRC at an early age, penetration resistance, shrinkage, tensile and ultrasonic pulse velocity (UPV) tests were performed. Test results indicate that paraffin oil well prevents the rapid water evaporation on the surface when the penetration resistance test of UHPFRC mortar was performed. The restrained shrinkage stress starts to develop when penetration resistance was 1.5 MPa. Thus, the time-zero of autogenous shrinkage measurements of UHPFRC was defined as when the penetration resistance becomes 1.5 MPa, this is 0.6 and 2.1 h before the initial and final sets, respectively. The tensile strength and elastic modulus were measured from near the initial set using tensile test apparatus and prediction models for tensile strength and elastic modulus of UHPFRC were proposed. Finally, the UPVs at the proposed time-zero, initial and final sets were defined and the very early age strength developments were also predicted using UPV.

초고성능 섬유보강 콘크리트(UHPFRC)의 재료 특성 및 예측모델: (I) 응결 및 수축 특성과 인장거동 평가

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

Autogenous Shrinkage in Plain Cement Mixtures

Determination of a realistic model for the estimation of autogenous shrinkage in plain cement mixtures has been an ongoing research among researchers in high performance concrete. While no standard test method exists for the determination of autogenous shrinkage, various researchers have designed different test methods for measurement of autogenous shrinkage. Current study involved the experimental determination of autogenous shrinkage using the test method developed by O.M.Jensen and co-workers, complimented with non-contact eddy current sensors. Measurements were conducted from as early as 1.5 hours from the time of casting. The samples were placed in a constant temperature chamber and the temperature of the sample was also monitored using a thermocouple. The study was carried out on plain cement mixtures at three water cement ratios of 0.25, 0.32 and 0.38. Measurements were also conducted on simple sealed prismatic samples but these measurements could only be collected after 24 hours of casting. The work is supplemented with CEMHYD3D simulations of the samples at similar water-cement ratios under sealed conditions so as to understand the development of the microstructure of the cement responsible for autogenous shrinkage. While experimental determination of internal relative humidity is quite difficult, data regarding chemical shrinkage, amount of water left and the development of the discontinuous capillary network from the simulations help to understand the determined experimental values of autogenous shrinkage. A detailed explanation on the causes of autogenous shrinkage and the basic mechanism responsible for it has been presented.