Chemical Shrinkage Test Research Articles

Experimental study of pure Class G cement hydration up to 150 °C and 50 MPa

A comprehensive experimental investigation of Portland cement hydration kinetics in a wide temperature range from 35 °C to 150 °C with pressure up to 50 MPa was performed by heat of hydration, chemical shrinkage and ultrasonic measurements. Increasing curing temperature was found to have a stronger acceleration effect during the main hydration period while increasing curing pressure had a stronger acceleration effect during the pre-induction period of cement hydration. By comparing chemical shrinkage test results with other methods of estimating cement degree of hydration, such as quantitative X-ray diffraction, non-evaporable water content measured by thermogravimetric analysis, as well as heat of hydration, it was observed that total chemical shrinkage of cement at complete hydration decreased with curing temperature from 35 °C to 75 °C and then stayed stable between 75 °C and 150 °C. Similarly, the P-wave velocity of cement (which is an indicator of physical and mechanical properties) as a function of hydration degree decreased with increasing curing temperature in the range between 35 °C to 75 °C, then remained relatively stable between 75 °C and 130 °C. The reduction of gel water content in C–S–H from 35 °C to 75 °C is believed to be the primary cause of these observed phenomena.

Sustainable approach to simultaneously improve the pozzolanic activity of sugarcane bagasse ash and the vinasse fertilization potential

The purpose of this study was to evaluate the viability of sugarcane bagasse ash as a sustainable supplementary cementitious material and its association with improving the fertilizing properties of vinasse, used as a leaching agent. Thus, a bagasse ash with low quartz contamination was divided into three parts: one kept in natura, one submitted to citric acid leaching and the third to vinasse leaching. After production, which was concluded with re-calcination and ultrafine grinding, the three ashes were characterized according to their chemical and mineralogical composition, particle size, porosity, density, and pozzolanic activity. Paste hydration with 20 wt% cement replacement by each ash was assessed in isothermal calorimetry and chemical shrinkage tests. The elemental and oxide composition of vinasse before and after leaching was also obtained. The results showed that vinasse leaching promoted an increase in specific surface area and pozzolanic activity of ash, comparable to that observed for citric-acid leaching procedure. Tests with pastes containing vinasse-leached ash confirmed the improvement in cement hydration. In addition, after leaching, vinasse exhibited a decline in heavy metal concentration, increased pH (neutralization) and macronutrient concentration. Thus, vinasse leaching improved the pozzolanic characteristics of ash, making vinasse a more environmentally friendly fertilizer.

Shrinkage characteristics of calcium sulphoaluminate cement concrete

Shrinkage is an important scientific and engineering issue in the study of cement concrete, involving the risk of cracking, safety and durability of the structure. For Ordinary Portland cement (OPC) concrete, capillary tension, represented by internal relative humidity, is normally considered as the main driving force of shrinkage. However, for calcium sulphoaluminate cement (CSA) concrete, it may be completely different. In the present paper, shrinkage performance of normal and high strength CSA concrete is experimentally investigated. Characteristics of shrinkage of CSA concrete comparing to OPC concrete are analyzed and the possible mechanisms are explored. The results show that development of shrinkage of CSA concrete since set obeys two-stage mode, fast growth stage before 2 h and a slowly developing stage after 2 h. In the initial 2 h after set of concrete, more than 85% of the total shrinkage at 28 days is finished. Development of internal relative humidity of CSA concrete also undergoes a moisture saturated stage and a decline stage since casting. In humidity decline stage, less than 15% of the shrinkage of 28 days is developed in the later age although the internal relative humidity is obviously decreased as well in this period. Water content and chemical shrinkage test further confirm that faster water consumption and larger chemical shrinkage are expected for CSA paste and also for CSA concrete, comparing to that of OPC paste or concrete. Hydration particle size test results reveal that the deformability of hydration products of CSA under drying is less than that of hydration products of OPC. This may partially explain why low drying shrinkage of CSA concrete is observed.

Chemical shrinkage of paste and mortar containing limestone fines

The effect of including limestone fine (LF) on the chemical shrinkage of cement paste and mortar is investigated. The cement was partially replaced with 0 to 20% (by weight) with LF. The water to cementitious material (CM) ratio was maintained at 0.45. In the mortar mixes, the proportion of sand (S) to CM was 1:2. In addition to the chemical shrinkage test, compressive strength and density of specimens were determined. The chemical shrinkage data were collected up to 28 days. However, for compressive strength and density, testing continued up to 90 days of water curing. There appears to be an increase in chemical shrinkage between 10 and 15% limestone for both paste and mortar mixes. The trend appears to be similar for the compressive and density results.

Factors Influencing the Hydration, Dimensional Stability, and Strength Development of the OPC-CSA-Anhydrite Ternary System.

Due to the advantages of high early strength and rapid setting, ternary systems consisting of ordinary Portland clinker (OPC), calcium sulphoaluminate (CSA) clinker, and anhydrite have broad application prospects. However, further studies need to be undertaken to find a more optimal mixing proportion of this ternary binder in order to meet basic performance requirements. In this paper, isothermal calorimetric tests, chemical shrinkage tests, drying shrinkage tests, and compressive strength tests were carried out to systematically identify the effect of the OPC/CSA ratio and anhydrite dosage on the hydration, mechanical property development, and dimensional stability of ternary binders. It was found that a higher CSA content leads to a higher cumulative hydration heat, a shorter acceleration period, and a delayed induction period, which can be ascribed to the retardation of C3S at a high aluminate concentration. However, a higher addition of anhydrite can retard the main peak of hydration despite promoting the intermediate peak and improving the hydration reaction rate. The drying shrinkage of blends decreases first along with the CSA proportion and then increases. Moreover, a higher anhydrite content mitigates the drying shrinkage and hinders the strength development. Finally, considering the properties of both the fresh and hardened binder, the ternary blends with 5% anhydrite and OPC/CSA ratios ranging from 3/7 to 2/8 were identified as most suitable for applications that require a high early strength, stable late strength, and small level of shrinkage.

Chemical Shrinkage of Low Water to Cement (w/c) Ratio CEM I and CEM III Cement Pastes Incorporating Silica Fume and Filler.

Chemical shrinkage (CS) is the reason behind early age cracking, a common problem for concrete with low water to cement ratios (w/c < 0.35) known as Ultra-High- and High-Performance Concrete (U-HPC). However, to avoid the crack development initiated by autogenous shrinkage, a precise measurement of CS is required, as the values obtained can determine the correct amount of internal curing agent to be added in the mixture to avoid crack formation. ASTM C1608 is the standardized method for performing CS tests. In this study, recommendations are provided to improve the reliability of results obtained with this standard method, such as good compaction of samples and the use of superplasticizer (SP) for low w/c ratios (≤0.2). Cement pastes with CEM I and CEM III have been tested at different w/c ratios equal to 0.2, 0.3 and 0.4 with and without the addition of superplasticizer. CS results following ASTM-C1608 dilatometry showed that the presence of mineral additions such as silica fume and filler reduced the chemical shrinkage, while CS increased with increasing w/c. Low w/c ratio pastes of CEM III had slightly higher CS rates than CEM I, while the opposite was noticed at higher w/c. SEM images illustrated the importance of a careful compaction and SP use.

Effects of temperature and water-to-cement ratio on autogenous shrinkage of oil well cement

The chemical shrinkage and corrugated tube test methods were used to study the shrinkage behaviour of Class G oil well cement with water-to-cement (w/c) ratios of 0.3 and 0.5, cured at temperatures from 15 to 60°C. The experimental results show that the typical linear shrinkage evolution curve of a cement slurry obtained by corrugated tube method have an obvious inflection point, beyond which the linear shrinkage increase is close to zero. The time at which the inflection point is observed decreases significantly with increasing curing temperature, but varies very little with w/c ratio. The inflection time also shows approximately linear correlation with the setting time of the cement (The two are almost equal for w/c=0.3). The degree of hydration corresponding with the initial and final setting time were estimated based on chemical shrinkage test results and the relationships between estimated volumetric bulk shrinkage and chemical shrinkage were analyzed.

Modelling of chemical shrinkage evolution with curing degree of a filled epoxy adhesive

An epoxy adhesive system, commonly used in wind turbine blade manufacturing, is experimentally investigated with respect to its chemical shrinkage behavior to show the shrinkage evolution within rotor blade production related process conditions. Therefore, a new test configuration is set up to record the resulting chemical shrinkage of the adhesive at cross-linking temperatures ranging from 20°C to 90°C. The respective conversion evolution is simulated under several temperature conditions through a curing kinetics model. This is generated with state of the art formulations, implementing test results from a differential scanning calorimeter (DSC). Moreover, the transformation of the curing degree to the corresponding glass transition temperature (Tg ) is performed through an experimentally based Di-Benedetto curve-fitting. By the combination of curing kinetics and chemical shrinkage test data, a model for the temperature and conversion dependant chemical shrinkage evolution during cure is developed. This is applied to a realistic curing cycle for adhesive materials in rotor blade production.

Measuring and modeling hydration kinetics of well cements under elevated temperature and pressure using chemical shrinkage test method

Well cements hydrate under challenging conditions of elevated temperature and pressure. A standard and readily accessible experimental method to follow the hydration kinetics of well cements under these conditions is lacking. In this study, we present a new method to measure the chemical shrinkage of cements, using an ultrasonic cement analyzer coupled with an external pump — two common equipment in well cements research laboratories. The method measures chemical shrinkage by following the flux of water into the sample to maintain constant pressure. Various experimental parameters such as leakage and sample geometry are carefully examined. Chemical shrinkage results on Class G and Class H cements are in good agreement with various sources, including reported chemical shrinkage, reported activation constants, hydration kinetics measured by alternative methods, and phase assemblage measurements on hardened paste. The method offers a promising new technique to help advance our fundamental knowledge on the hydration of well cements.

Characterization of the absolute volume change of cement pastes in early-age hydration process based on helium pycnometry

Based on detection technology of helium pycnometry, this study developed a novel approach for characterizing the absolute volume change of cement pastes in early-age hydration process. This method gives an accurate and continuous surveillance on the absolute volume change of cement pastes excluding all the empty pore space even below nm-scale. Traditional methods, such as chemical shrinkage test (based on ASTM C 1608), isothermal calorimetry test and X-ray diffraction (XRD) analysis, are also adopted for comparison and analyzation. It was found that the data obtained by chemical shrinkage test is discontinuous and inaccurate, the data gotten by isothermal calorimetry test is vague and unspecific, and the data gained by XRD analysis is discontinuous and unspecific. Compared with the traditional methods, the results captured by helium pycnometry are continuous, accurate and specific for describing the hydration process, especially the changing details of the absolute volume change. But at the same time, helium pycnometry has a good correspondence with the traditional methods, whose trends are almost the same. Based on the trends of the absolute volume change and heat flow, the absolute volume change of cement pastes in early-age hydration process was then divided into four periods (dissolution period, induction period, fast reaction period and stable period).

Modeling cement hydration by connecting a nucleation and growth mechanism with a diffusion mechanism. Part II: Portland cement paste hydration

Abstract A particle-based C3S hydration model with only three rate constants developed in Part I of this study is further developed and applied to Portland cement paste hydration. Experimental data are obtained with chemical shrinkage tests of cement pastes prepared with different water to cement (w/c) ratios (0.3–0.5), and cured at different temperatures (24°C–63°C) and pressures (0.69–51.7 MPa). The proposed model produces exceptionally good fits to test data. The fitted results indicate that the entire process of cement hydration can be modeled by connecting a nucleation and growth mechanism with a diffusion mechanism. Furthermore, the results reveal that the deceleration period of cement hydration may be due to the gradual transition of the rate-controlling mechanisms of different particles. The fitted rate constants generally follow basic chemical kinetics laws in terms of their dependencies on curing temperature and pressure, and appear to be largely independent of w/c ratio.

Special Section on Advances in Internally Cured Concrete

Special Section on Advances in Internally Cured Concrete

Chemical Shrinkage of Pastes Made with Shrinkage Reducing Admixtures

Shrinkage Reducing Admixtures (SRA) are being used more often in concrete structures in order to better control shrinkage cracks. High-performance concrete, nowadays with large application, has more proneness to crack at very early age due to the lower W/C. In this type of concrete, autogenous shrinkage is usually more important than drying shrinkage. Autogenous shrinkage is due to the volume decrease inherent to binder hydration reactions. The rate of these reactions is influenced not only by the type of binder but also by the presence of chemical admixtures. It is recognized that SRA delay the hydration, being a secondary effect of this type of admixtures. In this work changes on the degree of hydration of cement pastes with SRA and different binders are presented, using the chemical shrinkage test.

Measurement of Volume Change in Cementitious Materials at Early Ages: Review of Testing Protocols and Interpretation of Results

Early-age cracking in concrete bridge decks, pavements, and superstructure elements has served as the impetus for substantial research on early-age shrinkage in cementitious materials. Much of this research has indicated how mixture proportions, constituent materials, and construction operations can be altered to reduce the risk of cracking. Unfortunately, many unrestrained shrinkage-testing protocols do not provide a comprehensive picture of the early-age shrinkage exhibited by cementitious materials, especially those used in higher-strength concrete. In this paper, the authors review several early-age shrinkage testing procedures. A testing protocol is presented to show how chemical shrinkage can be measured by using buoyancy measurements. A comparison of the measured autogenous shrinkage is made by using four measurement methods: a sealed membrane, a corrugated tube, a noncontact measurement in a rigid mold, and the ASTM C 157 standard. The results of the autogenous and chemical shrinkage tests are compared with one another to describe fully early-age length change. It is shown that through careful experimentation and interpretation, the results of these tests can be completely correlated with one another. This can provide the end user with reliable test procedures to compare different paste compositions and different admixtures and can provide inputs for models that quantify cracking potential.

Measurement of Volume Change in Cementitious Materials at Early Ages

Early-age cracking in concrete bridge decks, pavements, and superstructure elements has served as the impetus for substantial research on early-age shrinkage in cementitious materials. Much of this research has indicated how mixture proportions, constituent materials, and construction operations can be altered to reduce the risk of cracking. Unfortunately, many unrestrained shrinkage-testing protocols do not provide a comprehensive picture of the early-age shrinkage exhibited by cementitious materials, especially those used in higher-strength concrete. In this paper, the authors review several early-age shrinkage testing procedures. A testing protocol is presented to show how chemical shrinkage can be measured by using buoyancy measurements. A comparison of the measured autogenous shrinkage is made by using four measurement methods: a sealed membrane, a corrugated tube, a noncontact measurement in a rigid mold, and the ASTM C 157 standard. The results of the autogenous and chemical shrinkage tests are compared with one another to describe fully early-age length change. It is shown that through careful experimentation and interpretation, the results of these tests can be completely correlated with one another. This can provide the end user with reliable test procedures to compare different paste compositions and different admixtures and can provide inputs for models that quantify cracking potential.

Three simple tests for selecting low-crack cement

Abstract On projects involving restrained concrete such as bridge decks, the risk of cracking can be reduced by selecting low-crack Portland cement as was done with the Rudolphstein Bridge in Bavaria. A test, RILEM TC 119 TCE 3, was used to establish the cracking risk from thermal contraction and autogenous shrinkage [ACI Monograph 11 (1998)]. No equivalent ASTM test exists. The new drying shrinkage cracking test, AASHTO 34 98 is not directly applicable to the early-age cracking problem in bridge decks as this cracking is caused by thermal contraction and autogenous shrinkage. This paper presents two methods, much simpler than the RILEM test, for estimating the cracking tendency of Portland cement: a 12-h semi-adiabatic compressive strength test, and a 12-h chemical shrinkage test. A simple drying shrinkage test using cement paste is also discussed. It is concluded that the strength test and the chemical shrinkage test measures the thermal cracking tendency of Portland cement and can be used to select low-crack Portland cement for important projects involving restrained concrete. The tests, particularly, the chemical shrinkage test, should be considered for inclusion in the Standard Performance Specification for Hydraulic Cement, ASTM C 1157. This is important because the United States is experiencing more cracking problems than in some other countries such as Germany where it has been reported that bridge deck cracking is not a problem [ACI Monograph 11 (1998)]. They have coarser cements and limit the cement content.

Thermal treatment and pozzolanic activity of Na- and Ca-montmorillonite

Samples of both untreated and calcined (at about 730, 830 and 930°C) Na- and Ca-montmorillonite, before and after having reacted with Ca(OH) 2 in the presence of simulated cement pore solution, were studied with XRD, SEM, EPMA and for chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the (un) calcined montmorillonite-cement mortars were studied with theological properties and compressive strength tests after reaction for 2, 7, 28 and 91 days. The study indicates that the montmorillonites are fairly good pozzolanic materials and calcination substantially improves their pozzolanic activity. A clear optimum calcination temperature is 830°C for both Na- and Ca-montmorillonite.

Thermal treatment and pozzolanic activity of sepiolite

Samples of standard sepiolite were calcined at 370, 570 and 830°C corresponding to the various stages of thermal reaction detected by DTA and TG. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated cement pore solution, were studied with XRD, SEM, EPMA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the raw and calcined sepiolite-cement mortars were studied with theology and compressive strength tests after reaction for 2, 7, 28 and 91 days at 40°C. The results indicated that sepiolite is rather inactive as a pozzolanic material and has high water demand. The calcination to 370 and 570°C does not upgrade it significantly. The most effective calcination temperature is 830°C, which increases the compressive strength of its mortar to 84% of the compressive strength of the reference ordinary Portland cement (OPC) mortar.

Thermal stability and pozzolanic activity of calcined illite

Standard illite (American Clay Society, IMt-1) was calcined at 650,790 and 930°C for 100 minutes. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated cement pore solution, were studied by DTA, TG (for raw illite), XRD, SEM, EMPA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the untreated and calcined illite-cement mortars were studied by theology (flow) and by a compressive strength test after reaction for 2, 7, 28 and 91 days. The current investigation revealed that illite has low pozzolanic activity. Dehydroxylation at 650°C does not upgrade it significantly. Further calcination at 790°C brings about considerable activation but it still does not qualify as a pozzolan. Calcination at 930°C produces the highest pozzolanic activity. Compressive strength of the mortar with 930°C illite is 79% of that of reference ordinary portland cement.