Measurement Of Chemical Shrinkage Research Articles

Hydration behavior and strength development of supersulfated cement prepared by calcined phosphogypsum and slaked lime

The effect of the content of calcined phosphogypsum (CPG) and slaked lime (SL) on the fluidity, setting time, and compressive strength of supersulfated cement (SSC) were investigated. The hydration mechanism of the SSC containing CPG and SL was examined through electrical resistivity, hydration heat, and chemical shrinkage measurements and thermodynamic modelling was performed to predict the phase assemblages. The results indicate that SSC with CPG delayed the early age hydration and prolongs its induction period. The effect of CPG on delaying hydration was apparent in SSC with 5 % SL. CPG in SSC promotes the formation of ettringite (AFt), while excess SL inhibits it. With the increase of CPG, massive gypsum is produced, leading to the rapid setting and a decrease in fluidity. Excess AFt contributes to expansion and cracking, resulting in a decrease in compressive strength. With the incorporation of SL, the pH value of the pore solution increases, which is beneficial to the stabilization of AFt, thereby increasing the compressive strength. The compressive strength of SSC containing 10 % CPG and 10 % SL reached up to 35.2 MPa after 180 d. The study reveals the mechanism of the effect of CPG and SL on SSC hydration and provides theoretical guidance for preparing SSC for engineering applications.

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.

Measuring chemical shrinkage of ordinary Portland cement pastes with high water-to-cement ratios by adding cellulose nanofibrils

Chemical shrinkage is an important way to study the hydration kinetics of cement. However, the measurement of chemical shrinkage for cement pastes with high water-to-cement ratio (w/c) faces a significant bleeding issue. This study demonstrates the use of cellulose nanofibrils (CNF) to create a stable structure that can support cement particles and let them be hydrated without settling. The measured chemical shrinkage curves for the 0.5 w/c cement pastes with and without CNF are very similar at early ages (e.g., 3 d), which implies that the chemical effect of CNF on cement hydration is small in the short term; therefore, the use of CNF allows study of chemical shrinkage for high w/c cement pastes at the early ages. The results show that with the increase of w/c, the main hydration peak is delayed and the post-peak stage is prolonged. In the long term (e.g., after 3 days), the measured chemical shrinkage for high w/c is higher than the low w/c. Similarly, the degree of hydration curves show that, with more water, cement hydration is eventually much enhanced.

The effects of seeding C3S pastes with afwillite

The addition of 1–4% s/s (dry solids by mass of C3S) of afwillite (C3S2H3) seeds to C3S pastes made with two different commercial polyacrylate-based superplasticizers (SP) allows the pastes to be cast at low water/C3S mass ratios (w/c) and overcomes the hydration retardation produced by the SPs. SP-free C3S pastes seeded with afwillite at an initial w/c of 0.50 gave about 30% lower 28-day compressive strengths than the unseeded controls, due to higher porosities. However, at w/c=0.35, with the addition of 0.4% s/s SP, the afwillite-seeded pastes gave similar or higher strengths than the unseeded controls at all ages tested. Hydration rate data obtained by chemical shrinkage measurements suggest that this is because the degrees of hydration of the C3S in the low w/c afwillite-seeded pastes made with added SP reach higher values than in the unseeded controls, compensating for the difference in density of the hydrates.

An innovative test apparatus for oil well cement: In-situ measurement of chemical shrinkage and tensile strength

An innovative apparatus has been developed in this study to cure and test oil well cement specimens under simulated down-hole conditions with high temperature and high pressure. The test apparatus can be used to monitor cement chemical shrinkage in real time and measure fluid pressure tensile strength under in-situ conditions, i.e. without changing the temperature or releasing the pressure of the specimen. This paper describes the basic principles of this newly developed test method and detailed configuration of the test apparatus. A series of tests were performed on different classes of oil well cement to evaluate the functionality of the test device. Specimens in groups of four were cured at temperatures ranging from 24 to 60°C and pressures ranging from 0.69 to 13.1MPa.

The studies of the effect of sulfates added as chromium(VI) reducers in portland cement

The calorimetric measurements were applied in testing the effect of some sulfates, used as Cr(VI) reducers in cement, as setting and hardening modifiers. The iron(II) sulfate is most commonly added as Cr reducer to cement on grinding. This was taken as a reference in the studies of the other potential chromium reducers, such as tin(II) and manganese(II) sulfates on cement hydration. The high percentage of admixtures was reduced steadily from very high overdosage—to find the possible effect of non-homogeneity resulted from the hygroscopic character of compounds used and to detect the possible products which can be formed—to relatively small quantity, as used in practice. The progress of cement hydration was investigated by calorimetry and chemical shrinkage measurements. The rheological properties of cement paste admixtured with iron, tin, and manganese sulfates were investigated, as well as the phase composition of hydrated pastes was studies by XRD. The compressive strength of the small paste cylinders was measured. Finally, the hydrated samples were subjected to the SEM observations. The tin sulfate showed the strongest retarding action as it was proved by calorimetry and chemical shrinkage data, as well as by strength and rheological measurements; however, at small quantities, this compound has a positive impact on setting and hardening. The detrimental effect of overdosed Mn and Fe sulfates due first of all to the formation of higher amount of ettringite at very early age was found. This can be proved additionally by the change of rheological parameters—higher yield stress and viscosity.

Thermo-mechanical characterisation of in-plane properties for CSM E-glass epoxy polymer composite materials – Part 1: Thermal and chemical strain

The in-plane thermo-mechanical properties and residual stresses of a CSM E-glass/Epoxy material are characterised through the use of DSC and TMA. The measured data is used to generate material models which describe the mechanical behaviour as a function of conversion and temperature. The in-plane thermal expansion coefficient (α) of the composite material decreases above the glass transition temperature (Tg), which is compensated by a higher out of plane deformation above Tg. Comparison of α and chemical shrinkage measurements suggests that chemical bonds between the polymer matrix and the glass fibres are formed prior to shrinkage of the epoxy matrix, i.e., at an early processing stage. This suggests that production of composites with low residual stresses requires focus on reactivity between the matrix and the sizing rather than the matrix cure properties. As a consequence, residual stresses in the composite material are mainly a result of restricted cure shrinkage rather than mismatch between thermal expansion coefficients.

Measurement of chemical shrinkage of cement paste: Comparison study of ASTM C 1608 and an improved method

Chemical shrinkage of cementitious materials has significant contribution to the early volume change of concrete, therefore, precise measurement of chemical shrinkage of cementitous materials is increasingly concerned. In the present study, measurement methods for chemical shrinkage were reviewed, especially for dilatometry method specified in ASTM C 1608. It was found that the precision and repeatability of ASTM C 1608 method were significantly influenced by the water to cement (w/c) ratio and the thickness of cement paste, which can be attributed to the generation of voids in the cement matrix and the restraint of formed particle skeleton structure, especially when low w/c ratio and/or high thickness of cement paste were used. By adding a magnetic stirring bar to prevent the formation of skeleton structure of cement paste, the chemical shrinkage measurement was simplified and presented superior precision and repeatability than ASTM C 1608 method, and the obtained results had better correlation with the calculated chemical shrinkage.

Mitigation of autogenous shrinkage in alkali activated slag mortars by internal curing

Alkali activated slag shows considerable promise as an environmentally friendly alternative to binders produced from ordinary portland cement. The shrinkage behavior of alkali activated slags, however, is not well understood, and is a hurdle to widespread adoption. The use of pre-wetted lightweight aggregate-based internal curing to mitigate shrinkage in slags activated by Na2CO3 solution or waterglass/NaOH solution has been investigated. Chemical shrinkage measurements were used to determine the amount of additional curing water needed by the mixtures, and autogenous and total shrinkage measurements used to determine the effects of internal curing on the overall shrinkage of the systems. Internal curing can completely mitigate autogenous shrinkage; however, in the systems examined here, drying shrinkage was the dominant shrinkage factor. In such a case, the benefits of internal curing are most clearly observed during the first 7 days.

E-modulus evolution and its relation to solids formation of pastes from commercial cements

Models for early age E-modulus evolution of cement pastes are available in the literature, but their validation is limited. This paper provides correlated measurements of early age evolution of E-modulus and hydration of pastes from five commercial cements differing in limestone content. A recently developed methodology allowed continuous monitoring of E-modulus from the time of casting. The methodology is a variant of classic resonant frequency methods, which are based on determination of the first resonant frequency of a composite beam containing the material. The hydration kinetics — and thus the rate of formation of solids — was determined using chemical shrinkage measurements. For the cements studied similar relationships between E-modulus and chemical shrinkage were observed for comparable water-to-binder ratio. For commercial cements it is suggested to model the E-modulus evolution based on the amount of binder reacted, instead of the degree of hydration.

Shrinkage determination of a reactive polymer with volumetric dilatometry

Several methods exist to determine the matrix volumetric shrinkage due to polymerisation/curing and thermal effects. A volumetric shrinkage test method that was further developed by Li et al. [C. Li, et al., In-situ measurement of chemical shrinkage of MY750 epoxy resin by a novel gravimetric method, Composites Science and Technology 64 (1) (2004) 55–64] is based on the buoyancy principle and allows monitoring of volumetric changes during the entire cure cycle. The aim is to use this test method for validation of cure shrinkage results obtained with Fibre Bragg gratings that were presented in a previous paper [P.P. Parlevliet, H.E.N. Bersee, A. Beukers, Measurement of (post-)curing strain development with fibre Bragg gratings, Polymer Testing, 29(3) (2010) 291–301.]. For that purpose, experiments have been conducted with a thermosetting polyurethane (turane) resin system. Even although the FBG and volumetric test set-ups resulted in different curing behaviour (different peak temperatures), the final linear shrinkage values were comparable.

Simultaneous measurements of heat of hydration and chemical shrinkage on hardening cement pastes

Isothermal calorimetry and chemical shrinkage measurements are two independent techniques used to study the development of hydration in cementitious systems. In this study, calorimetry and chemical shrinkage measurements were combined and simultaneously performed on hydrating cement paste samples. Portland cement pastes with different water to cement ratios and a cement paste containing calcium sulfoaluminate clinker and anhydrite were studied. The combined calorimetry/chemical shrinkage test showed good reproducibility and revealed the different hydration behavior of sealed samples and open samples, i.e., samples exposed to external water during hydration. Large differences between sealed and open samples were observed in a Portland cement paste with low water to cement ratio and in the calcium sulfoaluminate paste; these effects are attributed to self-desiccation of the sealed pastes. Once the setup is fully automatized, it is expected that combined calorimetry/chemical shrinkage measurements can be routinely used for investigating cement hydration.

In-situ measurement of chemical shrinkage of MY750 epoxy resin by a novel gravimetric method

A novel approach has been developed to measure in-situ chemical shrinkage of epoxy resins at the temperature of cure, during which the epoxy resins pass through liquid, rubbery and glassy states. A small sample of MY750/HY917/DY073 epoxy resin system, sealed in a thin-walled silicone bag, was suspended in a pot of silicone fluid and weighed independently of the silicone bath. The buoyancy of the sample was monitored as its density increases with respect to the constant density fluid during isothermal cures at three different temperatures. The relationship between the chemical shrinkage and degree of cure was deduced from a cure kinetics model for the resin. The good match of the results for the three different cure cycles suggests that chemical shrinkage is only a function of degree of cure regardless of time and temperature. A bi-linear relationship was fitted to the experimental data. The break point is at a degree of cure of about 28%, with corresponding chemical shrinkage of 3%. This point is linked to the gel point of the resin, which was measured as approximately 25% degree of cure in previous work. Total cure shrinkage of 6.9% for the MY750 resin system was obtained by extrapolating the results to a degree of cure of 100%. The method is sensitive, reliable and keeps the resin stress-free; therefore it should be applicable to a wide range of materials.

Monitoring Portland cement hydration: Comparison of methods

Various experimental methods of monitoring Portland cement hydration are compared. The methods are quantitative X-ray diffraction analysis (QXRD), measurement of non-evaporable water as loss on ignition and by thermogravimetry, conduction calorimetry and measurement of chemical shrinkage. Correlations between these different measures of hydration are obtained using samples of paste for three different Portland cements. The correlation between non-evaporable water and QXRD data was dependent on the chemical composition of the cement and shows that less water was chemically bound at early ages, for a given amount of cement reacted. A near-linear relationship was found between chemical shrinkage and QXRD data. The correlation between heat of hydration and QXRD data was approximately linear and not greatly affected by cement type.

Obtaining hydration data by measurement of chemical shrinkage with an archimeter

Obtaining hydration data by measurement of chemical shrinkage with an archimeter