Early-age Properties Research Articles

Effect of nano-calcium carbonate on early-age properties of ultra-high-performance concrete

In this study, the effects of nano-calcium carbonate (CaCO3) addition on the early-age properties of ultra-high-performance concrete cured at simulated cold and normal field conditions were investigated. The nano-CaCO3was added at rates of 0, 2·5, 5, 10 and 15% as a partial volume replacement for cement. Similar mixtures incorporating chloride- and non-chloride-based accelerating admixtures were also tested for comparison. Results indicate the high potential of nano-CaCO3to accelerate the setting and hardening process of ultra-high-performance concrete through providing nucleation sites, increasing contact points and increasing the effective water-to-cement ratio. Although nano-CaCO3exhibited a comparable or slightly lower accelerating effect to that of the chloride- and non-chloride-based accelerating admixtures, it brings a number of benefits to concrete production. These include the development of low-maintenance structures through eliminating the risk of steel corrosion induced by chloride-based accelerating admixtures, as well as a more environmentally friendly concrete through reducing the cement factor of ultra-high-performance concrete.

Can nanotechnology be ‘green’? Comparing efficacy of nano and microparticles in cementitious materials

Abstract The use of nano-sized particles in cementitious materials introduces a myriad of potential innovations from new functionality to enhanced mechanical performance, but such materials can be energy-intensive to manufacture. With increasing emphasis on sustainable development, it is important to investigate and understand benefits and costs of using nanomaterials compared to relatively less energy-intensive microparticles. The current research investigates the effect of chemically inert nano and microparticles (i.e., titanium dioxide (TiO 2 ) and calcium carbonate (limestone)) on early age properties and behavior of cement-based materials. Results indicate that the early age hydration rates, shrinkage, and pore structure of cement-based materials can be modified and optimized by tailoring the size of fillers. Life cycle analysis indicates that photocatalytic reactivity of TiO 2 could offset initial higher environmental impacts. Thus, optimally sized nanoparticles could revolutionize the construction industry by allowing tailoring of structure and properties of cement-based composites, with environmental sustainability preserved through the selection of lower embodied-energy particles.

Role of slag in microstructural development and hardening of fly ash-slag geopolymer

This paper presents the microstructural development and hardening rate of fly ash-slag geopolymers. The solid precursors are treated with a potassium hydroxide-silicate activator of modulus 1.25. Ultrasonic wave reflection and Proctor penetration methods are used to determine the rate of hardening. Microstructural development is investigated using SEM-EDS, and the reaction rate is monitored using semi-adiabatic calorimetry. Both UWR and Proctor penetration methods capture changes in the hardening rate due to changes in the reaction mechanism. An increase in the rate of hardening is observed with the addition of slag. It is concluded that the calcium that dissolves from slag significantly influences both early and late age properties, and the availability of free calcium ions seems to prolong fly ash dissolution and enhance geopolymer gel formation. It is proposed that the hardening process is initiated by the precipitation of C-A-S-H and that rapid hardening continues due to accelerated geopolymerization.

Effect of clinker phase distribution within cement particles on properties of a hydrating cement paste

SEM/X-ray images of cements in the Virtual Cement and Concrete Testing Laboratory were analyzed and used in simulations to investigate the effect of spatial distribution of clinker phases within particles on hydration and resulting properties. Percentages of the clinker phases actually consumed in the total hydrated clinker at any time during hydration (‘active phase content’s) are different than those measured on the unreacted powder (‘overall phase content’s), which may weaken predictions of the overall rate of hydration and property (heat and strength) development especially at early ages, and when hydration is incomplete. A demonstration in 2D of how ‘active phase content’s differ from the measured ‘overall phase content’s at different degrees of hydration, is provided as well as one in 3D, using a hydration model, for one of the cements. The influence of phase distribution on hydration and property development is discussed by comparing four different cases/microstructures hydrated under the same model conditions. For the same phase contents and fineness, differences in distribution have a significant effect on early-age properties but a lesser effect at later ages.

Study on Failure Criterion and Yield Criterion of Early-Age C20

The early-age concrete properties are the basis for structure nonlinear analyzed under construction structure period. But at present the study on early-age concrete is lagging behind which there is not suitabel theory. This paper takes early-age C20 concrete as an example to analysis the early-age concrete properties. According to the distribution characteristics of early-age C20 concrete experiment data in the octahedral stress space, using section function expression form, by the method of mathematical derivation and linear fitting, the failure criterion and the elastic yield criterion of early-age C20 concrete materials in the octahedral stress space are established. By comparison between failure criterion and elastic yield criterion of C20 concrete, the subsequent yield criterion could be derived based on the non-uniform isotropic strengthening criterion.

Effects of nano- and micro-limestone addition on early-age properties of ultra-high-performance concrete

In this study, the effects of micro- and nano-CaCO3 addition on the early-age properties of ultra-high-performance concrete (UHPC) cured at simulated cold and normal field conditions were investigated. The micro-CaCO3 was added at rates of 0, 2.5, 5, 10 and 15 %, while the nano-CaCO3 was added at rates of 0, 2.5, and 5 %, both as partial volume replacement for cement. Results indicate that micro-CaCO3 acted mainly as an inert filler, creating a denser microstructure and increasing the effective w/c ratio. In addition, nano-CaCO3 accelerated the cement hydration process through nucleation, and also acted as an effective filling material. Mixtures combining both micro- and nano-CaCO3 resulted in similar or enhanced mechanical properties compared to that of the control, while achieving cement replacement levels up to 20 %. Thus, through the use of micro- and nano-CaCO3, more environmentally friendly UHPC can be produced by reducing its cement factor, while achieving enhanced engineering properties.

The early age non-destructive testing of concrete made with recycled concrete aggregate

The increasing demand for concrete in construction places pressure on its constituent materials including aggregate. Attention has previously been turned to alternative aggregates, such as recycled concrete aggregate (RCA), to reduce the impact of quarrying. It is the aim here to investigate the very early age behaviour and properties of RCA concrete in relation to normal concrete using non-destructive testing. Ultrasonic pulse velocity (UPV) and surface hardness tests have been carried out on concretes made with different mix proportions. A system was set up which enabled the continuous measurement of UPV throughout the fresh and hardening stages. RCA concrete produced lower strength and UPV values than normal concrete. However, higher surface hardness was obtained for RCA concrete.Relationships have been established between strength and UPV, covering the period from immediately after mixing and up to 1day or 28days. This would enable more accurate assessments of important early age concrete strengths from UPV measurements. It has also been established that UPV measurements can be used to determine concrete setting.

Modification of cement-based materials with nanoparticles

This is a summary paper on the work being done at the Center for Advanced Cement-Based Materials at Northwestern University on the modification of cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles, and nanosilica. The rheological properties of clay-modified cement-based materials are investigated to understand the influence of nanoclays on thixotropy. The influence of the method of dispersion of calcium carbonate nanoparticles on rate of hydration, setting, and compressive strength are evaluated. And an in-depth study on the mechanisms underlying the influence of nanosilica on the compressive strength gain of fly ash–cement systems is discussed. The motivation behind these studies is that with proper processing techniques and fundamental understanding of the mechanisms underlying the effect of the nanoparticles, they can be used to enhance the fresh-state and hardened properties of cement-based materials for various applications. Nanoclays can increase the green strength of self-consolidating concrete for reduced formwork pressure and slipform paving. Calcium carbonate nanoparticles and nanosilica can offset the negative effects of fly ash on early-age properties to facilitate the development of a more environmentally friendly, high-volume fly ash concrete.

Effect of Natural Wollastonite Microfibers on Early-Age Behavior of UHPC

In this study, the effect of incorporating wollastonite microfibers in ultrahigh performance concrete (UHPC) on its early-age properties was investigated. Wollastonite microfibers were added at 0, 4, 8, and 12% as partial volume replacement for cement. Results show that the early-age properties of UHPC mixtures incorporating wollastonite microfibers are highly affected by the microfiber content and aspect ratio. Increasing the wollastonite microfiber content resulted in a compressive strength comparable to or higher than that of the control mixture without microfibers. Wollastonite microfibers reduced shrinkage strains and increased cracking resistance compared to that of the control mixture. However, no significant improvement in the flexural behavior was achieved with the addition of wollastonite microfibers because of a sudden rupture of microfibers within the matrix. Wollastonite microfibers can act as an internal restraint for shrinkage, reinforcing the microstructure at the microcrack level, and leading to an enhancement of the early-age engineering properties of UHPC matrix. Partially replacing cement with natural wollastonite microfibers leads to a reduction in the cement factor, which represents economic and environmental benefits.

Early-age properties, strength development and heat of hydration of concrete containing various South African slags at different replacement ratios

This research investigated fresh and hardened properties of concretes containing three different types of slag at three different replacement ratios and three different water/binder ratios. The three types of slag include ground granulated blastfurnace slag, ground granulated Corex slag and a ground granulated ferro-manganese arc furnace slag. Different methods for the assessment of slag hydraulic activity are compared, including chemical and physical characterisation of the various binders and binder blends, mortar compressive strength tests and heat of hydration tests, indicating the limitations of the various methods if used in isolation. The test results indicate that the use of the slags under investigation increases concrete workability at high water/binder ratios only. Setting times and 1-day strength values were strongly dependent on the slag replacement ratio. The influence of slag replacement level on compressive strength reduced over time. Strength development characteristics and long-term strength values were considerably different for different types of slag.

Monitoring early age property of cement and concrete using piezoceramic benderelements

Ultrasonic waves are commonly used for non-destructive evaluation of concretestructures. For fresh concrete, ultrasonic waves have also been used to monitorconcrete setting and strength development at early ages. However, the conventionalultrasonic test set-up typically needs access to the two opposite sides of concretestructures, which is not always possible for in situ field testing. In this paper,embedded piezoceramic bender elements are proposed to measure ultrasonic shear(S) waves in fresh cement paste, mortar and concrete. The shear wave velocitiesare obtained from B-scan images of a collection of recorded signals over time.Experimental results indicate that the shear wave velocity is closely related tothe setting time, and this relationship is independent of air void content andw/c of cement pastes. The low cost bender elements can also be of use to monitorthe setting of fresh concrete and the long term evaluation of hardened concrete.

Properties of Autogenous Shrinkage in High-Strength Mass Concrete According to Hydration Heat Velocity

The early-age properties and relationships between hydration heat and autogenous shrinkage in high-strength mass concrete are investigated through analysis of the history curves of hydration heat and autogenous shrinkage. To reduce the hydration heat velocity, micro encapsulated retarder (MR) that could retard cement reaction was applied. In the result of research, the hydration temperature and hydration heat velocity of high-strength mass concrete can be decreased with the reduction of size specimen and use of the retarder. A close relationship could be found between the hydration temperature and autogenous shrinkage; the higher the hydration heat velocity, the higher the autogenous shrinkage velocity and the greater the ultimate autogenous shrinkage.

Influence of metakaolin and silica fume on the heat of hydration and compressive strength development of mortar

In this study, two metakaolins (MK1 & MK2) were investigated for use as supplementary cementitious materials in cement-based systems. The MK vary in their surface area (17 to 19 m 2/g), but are almost similar in chemical composition. Total of four series of mortar mixes were made. First was control mix. Second and third mixes contained 10% of each of the MK as partial replacement of cement. In fourth mix, cement was replaced with 10% silica fume (SF). Water-to-cementitious materials ratio was kept constant as 0.36. Performances of MK mixes were compared with control mix, and mixes incorporating SF. Tests were conducted for early-age properties of fresh mortar and compressive strength. Early age investigation was aimed to determine the reactivity (temperature and heat of hydration of MK), and its effect on fresh mixture (slump flow). Test results have indicated that (i) blended mortar with MK can reach higher temperature with respect to 100% ordinary Portland cement; (ii) MK exhibits lower pozzolanic activity than SF. Hydration heat of SF is greater than that of MK; (iii) it is supposed that there are three elementary factors which influence the contribution that MK makes to mortar strength when it partially replaces cement in mortar. These are the filler effect, the acceleration of ordinary Portland cement hydration and the pozzolanic reaction of MK with calcium hydroxide.

Analysis of hydration heat and autogenous shrinkage of high-strength mass concrete

The early-age properties and relationships between hydration heat and autogenous shrinkage in high-strength mass concrete of different mixture proportions are investigated through analysis of the history curves of hydration heat and autogenous shrinkage. The hydration temperature and hydration heating velocity (HHV) of the concrete were found to increase with increases in specimen size and decrease when the concrete contained a retarder, fly ash (FA) and ground granulated blast-furnace slag (GGBS). Even in samples of the same mixture proportion, autogenous shrinkage was noted to become greater as the inner temperature increased. The autogenous shrinkage of high-strength mass concrete containing FA and GGBS was lower than that of ordinary Portland cement high-strength mass concrete. The autogenous shrinking velocity of concrete increased as the size of the specimen increased and decreased when the concrete contained a retarder, FA and GGBS. Finally, a close correlation was found between the hydration temperature and autogenous shrinkage at an early age: a higher HHV and a larger HHV–maturity factor led to greater autogenous shrinkage.

Early-age properties of concrete: overview of fundamental concepts and state-of-the-art research

The long-term performance of concrete structures is affected to a large extent by the properties and behaviour of concrete at early age. However, the fundamental mechanisms affecting the early-age behaviour of concrete have not yet been fully understood. This is due to the various highly interrelated factors influencing it, and the complexity of testing techniques needed for its investigation. With modern developments in concrete technology, it has become essential to evaluate the influence of these interrelated factors and their implications for the service life of concrete structures. Thus, a more fundamental approach for investigating the early-age behaviour of concrete, along with more reliable testing techniques, is required. This paper provides a critical overview of research on the mechanisms that affect the properties of concrete and its performance at early age. It provides useful, concise and coherent information on the behaviour of concrete at early age, which should enhance the understanding of the implications of such behaviour on the service life performance of concrete structures.

Influence of geometric factors on the punching load resistance of early-age fibre reinforced shotcrete linings

Understanding the early-age properties of fibre reinforced shotcrete (FRS) is critical to the accurate estimation of the time to safe re-entry under freshly sprayed FRS linings. Previous research in the field has indicated that shear failures dominate early-age load resistance and thereby govern the performance of a lining during the first few hours after spraying. This investigation has examined the influence of several geometric variables on shear resistance in a punching mode of failure. In particular, the research has addressed the influence of the size, shape, eccentricity, and inclination of punching loads on the apparent shear strength of an early-age fibre reinforced shotcrete (FRS) lining.

The origin of early age expansions induced in cementitious materials containing shrinkage reducing admixtures

Studies on the early-age shrinkage behavior of cement pastes, mortars, and concretes containing shrinkage reducing admixtures (SRAs) have indicated these mixtures frequently exhibit an expansion shortly after setting. While the magnitude of the expansion has been noted to be a function of the chemistry of the cement and the admixture dosage; the cause of the expansion is not clearly understood. This investigation uses measurements of autogenous deformation, X-ray diffraction, pore solution analysis, thermogravimetry, and scanning electron microscopy to study the early-age properties and describe the mechanism of the expansion in OPC pastes made with and without SRA. The composition of the pore solution indicates that the presence of the SRA increases the portlandite oversaturation level in solution which can result in higher crystallization stresses which could lead to an expansion. This observation is supported by deformation calculations for the systems examined.

Application of Fiber Bragg Grating Sensor to Monitor Early Age Deformation of High Performance Concrete

This paper presents a method to monitor the early age properties of high performance concrete (HPC) specimens successfully by embedded fiber bragg grating (FBG) monitoring system. The results show that the deformation increases rapidly within the first 30 hours after HPC casting. And its value is up to 65 µε and 84µε for two specimens respectively. As for the durability and permeability of HPC, early age deformation of HPC is pretty high and can not be neglected. Meanwhile, temperature compensation technique for FBG strain sensor has been put forward, and it is applied to measure early age deformation and temperature of HPC beam in situ simultaneously. The monitoring technique used here can be extended to concrete early age behavior monitoring in mass concrete structure with any size.

Influence of limestone content, gypsum content and fineness on early age properties of Portland limestone cement produced by inter-grinding

Abstract This paper examines the behavior of Portland limestone cements (PLCs) made by inter-grinding clinker, gypsum and limestone in a full size-cement plant, while varying the content of limestone filler (LF – 0% and 24%), content of gypsum (GC – 2.5% and 5.0%) and PLC fineness, measured as that fraction retained on a 45 μm sieve (R45 – 5% and 18%). The influence of the combined action of these variables on the particle size distribution (PSD) and early age properties of blended cement was studied using a 23 experimental design. Fineness evaluated by the parameters of the Rosin–Rammler–Springer–Bennett (RRSB) distribution function shows that the uniformity index (n-parameter) depends strongly on LF content; while the characteristic diameter (x′-parameter) depends on R45 and LF content. As for the inter-grinding process, water demand is reduced by incorporation of LF and increased by reduction of R45, producing a compensation. Setting time is mainly affected by R45; LF produces a few modifications and the influence of gypsum content and gypsum–limestone interaction are not as obvious. Calorimetry studies show that LF decreases the height of the main peak and the total heat released, while gypsum content modifies the time of acceleration and the post-peak hydration, specifically for fine cements. In accordance, chemical shrinkage decreases when R45, LF content and gypsum content increase. Up to 2 days, strength is mainly governed by the R45 and the LF in PLC, which act inversely. At early ages, the influence of gypsum content on early properties increases up to 48 h. XRD analysis shows its stimulation of calcium silicate hydration during the first hours and ettringite formation after 24 h.

Early age properties of cementitious materials by electrical resistivity measurement

Three cement pastes were prepared with the fixed water-binder ratio and different fly ash contents. The compression test and electrical resistivity measurement of the paste mixes were conducted during 48 h. The changes of the CH content and the non-evaporable water content in the cement-fly ash hydration systems with time were obtained by the thermal gravimetric analysis. The experimental results show that dilution effect of fly ash as micro-filler is dominant mechanism before 48 h, which appears to decrease in the CH content and the non-evaporable water content, also in compressive strength and electrical resistivity, with the increase of fly ash replacement. The relationships between CH content, non-evaporable water content and electrical resistivity show that electrical resistivity can be the indicators of hydration products CH and non-evaporable water. The correlation of the compressive strength fc and the electrical resistivity ρ can be obtained as fc=8.3429 ρ = 6.7088 for the period of 48 h. The early age compressive strength can then be predicted by electrical resistivity measurement.