High Performance Cement Paste Research Articles

Dynamic modulus characteristics and prediction model of semi-flexible materials filled with high-performance cement paste

The dynamic modulus of asphalt mixture is an important factor in the design of asphalt pavement, and many scholars have proposed different models for estimating the dynamic modulus of asphalt mixture, but there are almost no studies on the prediction of the dynamic modulus of semi-flexible materials. In order to analyze and estimate the dynamic modulus of semi-flexible materials, we set up a high-performance cementitious paste (HPCP) semi-flexible material and a reference group Stone Mastic Asphalt (SMA-16) under multiple conditions, first measured its dynamic modulus in the laboratory, and analyzed the dynamic modulus characteristics of the material, and then used the equation the estimation equation proposed by Witczak et al. (Witczak1-37A) as a benchmark to introduce a new parameter, grouting mass ratio (Pb) to develop a Witczak-G prediction model to compare and validate the predicted dynamic modulus with the measured values. The results show that compared with SMA-16, HPCP semi-flexible material exhibits higher dynamic modulus and lower phase angle, and its temperature sensitivity and deformation resistance are significantly better than those of SMA-16. Under the influence of porosity and Pb factor, the dynamic modulus is positively correlated with both factors, and the phase angle increases first and then decreases, showing strong elastic properties. In this paper, we propose a dynamic modulus prediction model based on viscosity and Pb, Witczak-G, which predicts the highest coefficient of determination (R2) of the predicted dynamic modulus as high as 0.99 after initial fitting and validation, which indicates that the Witczak-G model is suitable for predicting the dynamic modulus of semi-flexible materials injected with HPCP.

Preparation and properties of porous rice husk ash for internal curing of high performance cement pastes

To address the challenges posed by significant autogenous shrinkage in high-performance concrete and mitigate the adverse effects of conventional internal curing materials on its mechanical properties, this study explored the potential use of rice husk ash (RHA) as internal curing materials. The research investigated the impact of combustion regime (combustion temperature and dwelling time) and the milling process on the microstructure and physical-chemical properties of RHA. Moreover, the effect of RHA on autogenous shrinkage, compressive strength, and microstructure in cement pastes were also reported. Experimental results demonstrated that the combustion regime and milling time could significantly affect the pore structure, particle size and pozzolanic activity of RHA. RHA had good potential for internal curing when it was burned at 600°C for 1 h and milled for 15–30 min. RHA released the entrained water after 12 h to slow down the depletion of free water, and thus inhibited the development of self-drying and autogenous shrinkage. The 168 h shrinkage was reduced by 56.8 %, 62 %, and 51.8 %, respectively when the milling time increased to 30 min. Moreover, the addition of RHA with a smaller particle size could refine the microstructure of matrix and enhance the compressive strength due to its higher pozzolanic activity. These findings suggest promising applications for RHA as an effective internal curing material in high-performance cementitious materials.

Relevance of Specific Surface of Mixed Oxide Derived from Layered Double Hydroxides on the Rheological Properties and Porosity of Cement Pastes.

Cement-based products are the synthetic materials most used by humans, with consequent environmental impacts. One strategy that can assist in mitigating the adverse environmental effects of these materials involves the incorporation of multifunctional nanostructured additives. The objective of this work was to demonstrate the efficacy of incorporating mixed oxides (MO) derived from layered double hydroxides (LDH) to control the rheology and porosity of cement-based matrices. Thermal aging of LDH enabled the preparation of MO with different specific surface areas (SSA) for incorporation in different amounts in Portland cement. A low proportion of MO and low SSA increased workability by 22%. In contrast, a high proportion of MO and high SSA led to a 2.4-fold acceleration of cement consolidation and a 36.9% decrease of the porosity of the composite. These features could be attributed to additive-matrix interactions, with the LDH memory effect playing key roles in the cement crystal seed process and in competition for the absorption of free water within the cement paste. Therefore, the unprecedent results obtained suggest that the quantity and SSA of MO are key parameters to fine-tune the paste rheology and structure of hidrated cement. The MO materials showed easy adaptability and excellent potential for use as multifunctional additives in the production of eco-friendly, high-performance cement paste formulations with controllable properties according to the desired application.

Investigation on effect of colloidal nano-silica on the strength and durability characteristics of red mud blended Portland cement paste through tortuosity

A novel binder system for cement-based composites depending upon the strength and durability characteristics is introduced in this study. The possibility of calcined red mud cement pastes with and without colloidal nano-silica (CNS) over Ordinary Portland Cement paste (OPC) at three W/B ratios (0.3, 0.4, 0.5) is evaluated. The optimum percentage of cement replacement by red mud (15%) was selected from compressive strength values of different cement replacements (5%, 10%, 15%, and 20%). Colloidal nano-silica (CNS) was added at 0.5%, 1%, 1.5%, and 2 % to the selected red mud cement paste. Water absorption, sorptivity, resistance to sulfate attack, and resistance to acid attack tests were conducted for optimum red mud cement paste with and without CNS. The experimental results are explained based on tortuosity with empirical formulas and mathematical models of pore network distribution. The tortuosity is directly proportional to the inter-connectivity of the pores. The mixes with 15% calcined red mud and 1.5% CNS replacement performed better strength and durability at all W/B ratios. The mix (R15NS1.5) with minimum tortuosity value results in the higher overall performance of the paste. The mixes with a 0.3 W/B ratio give high-performance cement paste compared to higher W/B ratios.

Influence of HRWR molecular weight and polydispersity on rheology and compressive strength of high-performance cement paste

This study’s objective is to investigate the effect of the molecular weight (Mw) and polydispersity of different high-range water reducer (HRWR) types on the rheology and strength development of high-performance cement paste. Polynaphthalene sulphonates (PNS) and polycarboxylate (PCE) HRWR types with molecular weights ranging from 11,857 to 31,232 Da were investigated. The interactions between HRWR and cement particles were evaluated in terms of hydration kinetics, flow curves, viscoelastic properties, as well as compressive strength development. The investigated mixtures were proportioned with water-to-cement ratios (w/c) of 0.35 and 0.42. The obtained results showed that 0.35 w/c mixtures with a high molecular weight and low polydispersity index HRWR exhibited greater dispersing ability and compressive strength development but lower build-up kinetics. For a given HRWR type, the ideal Mw to ensure the best rheological performance and strength development is identified.

Early-age hydration process and autogenous shrinkage evolution of high performance cement pastes

This paper presented a comprehensive study on the early-age hydration process and autogenous shrinkage evolution of high performance cement pastes. The early-age hydration process of cement pastes was analyzed by combining 1H nuclear magnetic resonance relaxometry (1H NMR) with isothermal calorimetry. The hydration degree was contrastively analyzed by using 1H NMR and thermogravimetry analyses (TGA). Moreover, the relationship between the free water consumption process and autogenous shrinkage for cement pastes was revealed. Results showed that a magnetism-heat (M − H) model could be established according to the correspondence between free water consumption rate and hydration exothermic rate, which divided the early-age hydration process of cement pastes into four periods. The initial setting time was the onset that free water signal fraction started to drop, after this moment, the consumption rate of free water was increased and more hydration products were generated. After about final setting time, the weighted mean relaxation time of the free water sharply decreased, and the pore structure of cement pastes was gradually refined. The hydration degree (α) of cement calculated by 1H NMR and TGA showed good agreement, with the error of α values less than 2% after initial setting time. Furthermore, cement paste with a lower water/cement ratio showed higher autogenous shrinkage and lower free water signal fraction, but they did not show a good linear correlation with each other throughout the hydration process.

Microstructural refinement of cement paste internally cured by polyacrylamide composite hydrogel particles containing silica fume and nanosilica

Supplementary cementitious materials were incorporated into hydrogel-based internal curing agents to improve the hydration, microstructure, and ultimately strength of internally cured high-performance cement paste. Polyacrylamide composite hydrogel particles containing amorphous silica – either silica fume or nanosilica – and two different polymer network crosslink densities were synthesized and incorporated into cement paste. The presence of silica and low crosslink density increased the absorption capacity of the particles in pore solution. Micrographs of internally cured paste indicated a significant improvement in hydrogel-related void-filling ability and an increase in void size for low crosslink density particles containing silica. Compressive strength and electrical resistivity increased at later ages for paste samples containing particles with higher silica dosage. The relationship between extent of hydration, void size, and void-filling activity was found to strongly influence the paste's long-term strength and is thus an important structure-property relationship to consider when selecting hydrogels for internal curing purposes.

The effect of nano-MgO on the setting time, autogenous shrinkage, microstructure and mechanical properties of high performance cement paste and mortar

Many studies have targeted the application of micro-size MgO to reduce autogenous shrinkage in cement based materials. However, there is little knowledge the effect of nano-MgO on the mechanical, durability and microstructure properties of high-performance cement-based materials. In this paper, the properties of cement pastes and mortars with nano-MgO were experimentally investigated. 2.5%, 5.0% and 7.5% nano-MgO by weight of binder were used in mortar and paste mixtures. While the setting time and the volumetric autogenous shrinkage tests were carried out in paste mixtures, the heat of hydration, 7 and 28days compressive strength, ultrasonic pulse velocity (UPV) and 28days linear autogenous shrinkage test were carried out in mortar mixtures. In addition, Scanning Electron Microscopic (SEM) observations were also made to evaluate the effect of nano-MgO on microstructure. It was concluded that nano-MgO had a significant effect on the fresh and hardened properties of cement pastes and mortars. Generally, nano-MgO increased the compressive strength (about up to 8%). Nano-MgO decreased autogenous shrinkage and setting time decreased with an increased in use of nano-MgO. The final hydration heat of the control mixtures and the nano-MgO mixtures are almost the same. Nano-MgO can be used as an expanding additive.

Comprehensive service properties evaluation of composite grouting materials with high-performance cement paste for semi-flexible pavement

In this paper, high-performance cement pastes (i.e. h2 and h3) and pure cement paste (s) are respectively grouted into matrix asphalt mixtures (porous asphalt concrete 13, PAC-13) to service as semi-flexible pavement materials, and the comprehensive service properties of these composite grouting materials (H2, H3 and S), including mechanics feature and pavement performance are measured and compared with those of the traditional dense-graded asphalt concrete. Test results show that these composite grouting materials have similar mechanics characteristics, and H2 and H3 possess better pavement performance and durability than S. From the contribution of two-phase material (matrix asphalt mixture and grouting material) of composite grouting material, it can be concluded that both contributive efficiency and contributive rate of matrix asphalt mixture are lower than those of the grouting material. The uniaxial compressive strength of composite grouting materials approaches to that of the grouting material, which is much higher than that of asphalt mixture (matrix asphalt mixture and AC-13); while, the compression resilient modulus of composite grouting materials quite approaches to that of the asphalt mixture. To meet the requirements on moisture susceptibility of dense-graded asphalt concrete, the air void of matrix asphalt mixture should reach 21% for grouting high-performance cement pastes, and 24% for grouting pure cement paste.

Design and performance validation of high-performance cement paste as a grouting material for semi-flexible pavement

Semi-flexible pavement (SFP) has been applied in highway engineering for its good pavement performance. Many researches have been conducted on the performance differences between traditional pavement and SFP, but rarely focus on the composition of SFP materials, especially the composition of grouting materials. Therefore, this paper presents the study of composition design and performance validation of high-performance cement paste (HPCP) mixed with different types and dosages of additives as the grouting material for SFP. Results show that TH-928 polycarboxylate superplasticizer, UEA expansion admixture and ZY-99 saponin air-entraining agents have the different influences on the fluidity, strength and drying shrinkage of HPCP, and HPCP show good working capability with the compound addition of the three additives. Finally, the grouting materials were grouted into the matrix asphalt mixture to prepare SFP materials. The indexes, such as the grouting volume in per unit area, grouting depth and 7d residual porosity, were proposed to verify the grouting ability of selected materials. The verification results show that HPCP has the better grouting ability.

Innovative hybrid curing method for accelerating the strength of high-performance cement paste using microwave heating coupling with low-pressure processing

In this study, cementitious materials (here defined as a high-performance cement paste produced by mixing Type 1 Portland cement with an effective amount of water) were manufactured in accelerated conditions using microwave-assisted low-pressure processing (i.e., accelerated curing). Based on the concept that the hydration reaction of cementitious materials comprises three main periods—a dormant period, an acceleration period, and a deceleration period—process parameters were determined for the most effective period (acceleration) for producing paste via microwave processing. The time-dependent dielectric characteristics of the cementitious paste and the water–cement ratio by mass influenced the temperature, i.e., caused it to increase, and the properties of the microwave-cured paste. The results show that the use of microwave-assisted low-pressure processing improved the paste’s mechanical properties. Specifically, microwave energy can accelerate compressive strength development 15min after the completion of microwave-assisted low-pressure curing. With a delay time of 60min, microwave energy can process the paste almost a day faster than water curing, which is the standard method for curing paste. The use of microwave energy, therefore, can significantly reduce the required energy and production time in the manufacture of high-performance paste.

Numerical Simulation of Autogenous Shrinkage in High-Performance Cement Paste Based on a Multi-Component Hydration Model

Autogenous shrinkage is the term for the bulk deformation of a closed, isothermal, cement-based material system not subjected to external forces. It is associated with the internal volume reduction of cement/water mixture in the course of the hydration process. However, addition of blended components to cement, especially such as fly ash or silica fume, for the high-performance concrete will lead to a densification of the microstructure. The autogenous shrinkage deformation will increase and the following autogenous shrinkage crack will do harm to durability of concrete structure. In this paper, numerical simulation is suggested to predict autogenous shrinkage of high performance cement paste. The simulation is originated from a multicomponent hydration model. The numerical program considers the influence of water to cement ratio, curing temperature, particle size distribution, cement mineral components on hydration process and autogenous shrinkage. The prediction result agrees well with experiment result.

On the mechanism of polypropylene fibres in preventing fire spalling in self-compacting and high-performance cement paste

With the increasing application of self-compacting concrete (SCC) in construction and infrastructure, the fire spalling behavior of SCC has been attracting due attention. In high performance concrete (HPC), addition of polypropylene fibers (PP fibers) is widely used as an effective method to prevent explosive spalling. Hence, it would be useful to investigate whether the PP fibers are also efficient in SCC to avoid explosive spalling. However, no universal agreement exists concerning the fundamental mechanism of reducing the spalling risk by adding PP fiber. For SCC, the reduction of flowability should be considered when adding a significant amount of fibres. In this investigation, both the micro-level and macro-level properties of pastes with different fiber contents were studied in order to investigate the role of PP fiber at elevated temperature in self-compacting cement paste samples. The micro properties were studied by backscattering electron microscopy (BSE) and mercury intrusion porosimetry (MIP) tests. The modification of the pore structure at elevated temperature was investigated as well as the morphology of the PP fibers. Some macro properties were measured, such as the gas permeability of self-compacting cement paste after heating at different temperatures. The factors influencing gas permeability were analyzed. It is shown that with the melting of PP fiber, no significant increase in total pore volume is obtained. However, the connectivity of isolated pores increases, leading to an increase of gas permeability. With the increase of temperature, the addition of PP fibers reduces the damage of cement pastes, as seen from the total pore volume and the threshold pore diameter changes. From this investigation, it is concluded that the connectivity of pores as well as the creation of micro cracks are the major factors which determine the gas permeability after exposure to high temperatures. Furthermore, the connectivity of the pores acts as a dominant factor for temperatures below 300 °C. For higher temperatures micro cracks are becoming the major factor which influences the gas permeability.

Phase distribution and microstructural changes of self-compacting cement paste at elevated temperature

Self-compacting concrete, as a new smart building material with various advanced properties, has been used for a wide range of structures and infrastructures. However little investigation have been reported on the properties of Self-compacting when it is exposed to elevated temperatures. Previous experiments on fire test have shown the differences between high performance concrete and traditional concrete at elevated temperature. This difference is largely depending on the microstructural properties of concrete matrix, i.e. the cement paste, especially on the porosity, pore size distribution and the connectivity of pores in cement pastes. In this contribution, the investigations are focused on the cement paste. The phase distribution and microstructural changes of self-compacting cement paste at elevated temperatures are examined by mercury intrusion porosimetry and scanning electron microscopy. The chemical decomposition of self-compacting cement paste at different temperatures is determined by thermogravimetric analysis. The experimental results of self-compacting cement paste are compared with those of high performance cement paste and traditional cement paste. It was found that self-compacting cement paste shows a higher change of the total porosity in comparison with high performance cement paste. When the temperature is higher than 700 °C, a dramatic loss of mass was observed in the self-compacting cement paste samples with addition of limestone filler. This implies that the SCC made by this type of self-compacting cement paste will probably show larger damage once exposed to fire. Investigation has shown that 0.5 kg/m 3 of Polypropylene fibers in the self-compacting cement paste can avoid the damage efficiently.

Influence of limestone powder used as filler in SCC on hydration and microstructure of cement pastes

Abstract In recent years, self-compacting concrete (SCC) has gained wide application in the construction industry. As for high performance concrete (HPC) and traditional concrete (TC), the microstructural properties of SCC are the main factors, which determine the material properties, i.e. the mechanical properties, transport properties and the durability behaviour. In order to investigate the development of the microstructure of SCC, the microstructural parameters of the paste including porosity, pore size distribution and phase distribution are determined by means of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) are used to identify the phase constituents. These parameters as studied for self-compacting concrete are compared with high performance concrete and traditional concrete. The specimens of self-compacting cement paste (SCCP) are made with water/binder ratio 0.41 and 0.48, the high performance cement paste (HPCP) with w/c 0.33 and traditional cement paste (TCP) with w/c 0.48. The measurements are performed at different hydration stages, i.e. at 1, 3, 7, 14, 28 and 56 days. The result of this research shows that the pore structure, including the total pore volume, pore size distribution and critical pore diameter, in the SCCP is very similar to that of HPCP. The fact that limestone powder does not participate in the chemical reaction was confirmed both from thermal analysis and BSE image analysis.

Internal relative humidity distribution in high-performance cement paste due to moisture diffusion and self-desiccation

This investigation was carried out to study internal relative humidity (IRH) distribution of cement paste made with different water / cement ratios (w / c) and mineral admixtures in isothermal drying conditions. IRH changes in cement paste resulting from self-desiccation and moisture diffusion, respectively, at different ages were studied. The change laws of IRH in cement paste resulting from combining moisture diffusion with self-desiccation were discussed. The results indicate that IRH reduction of cement paste with w / c higher than 0.4 is mainly affected by moisture diffusion. However, IRH reduction of cement paste with w / c no higher than 0.4 is controlled by both moisture diffusion and self-desiccation. With the decrease of w / c, IRH reduction of cement paste resulting from self-desiccation increases, and IRH reduction resulting from moisture diffusion decreases at a given age. IRH decrement of cement paste incorporated with silica fume and ground blast-furnace slag is higher than that of control paste. w / c and the distance to the exposed surface play a significant role in IRH change resulting from moisture diffusion in isothermal drying condition. Change laws of IRH in cement paste with silica fume due to moisture diffusion considering self-desiccation are different from those in cement paste without silica fume.

Autogenous relative humidity change and autogenous shrinkage of high-performance cement pastes

In this paper, the effects of water to cementitious material ratio (w/cm), silica fume (SF) and ground blast-furnace slag (GBFS) on autogenous relative humidity (RH) change and autogenous shrinkage (AS) of high-performance cement pastes were studied. The mechanism of self-desiccation caused by mineral admixture and reduction of w/cm were studied by the parameters of mineral admixture self-desiccation-effect coefficient k and efficient w/cm r e proposed. Furthermore, the relationship between autogenous RH and AS of high-performance paste was established. The results indicate that w/cm is a chief factor that affects autogenous RH change and AS of cement pastes. The lower the w/cm of paste is, the more reduction the autogenous RH and the increment of AS are. SF increases autogenous RH reduction and AS increment of cement paste at early ages, and GBFS increases autogenous RH reduction and AS increment at later ages. The effect of mineral admixtures on autogenous RH change of paste resulting from self-desiccation can be reflected effectively by the nonlinear equation with the parameters of k and r e . There exists a good linear correlation between autogenous RH change and AS of cement pastes.

Comportement au feu des bétons

ABSTRACT Within the framework of the study of concrete structures subjected to fire, a theoretical and experimental work has been achieved. The aim of this study is to investigate and to model the damage mechanisms of concrete after exposure to high temperature. The multiphase Numeral Concrete Model and the damage model, MODEV, implemented on finite element software SYMPHONIE, were used simultaneously to model the thermal damage of concrete exposed to high temperature. In order to validate the thermal damage model, an experimental investigation was carried out. The measurement of the mechanical characteristics of high performance cement paste and high performance mortar specimens were performed by 3 points bending tests after heating/cooling stage at 120, 250 and 400°C.

Performance of new viscosity modifying admixtures in enhancing the rheological properties of cement paste

The use of viscosity modifying admixtures (VMA) has proved to be very effective in stabilizing the rheological properties and consistency of self-compacting concrete (SCC). SCC is known for its excellent deformability, high resistance to segregation and use, without applying vibration, in congested reinforced concrete structures characterized by difficult casting conditions. Most of the commercial VMAs currently available in the market are costly and increase the price of such a concrete. Identification or production of new low-cost VMA is then essential. This paper presents the performance of four new polysaccharide-based VMAs in enhancing the rheological and consistency properties of cement paste. The study of the rheological properties and consistency of cement paste to screen the dosage and type of new VMA to be used in SCC is a promising approach. Investigation was carried out on cement pastes with combinations of various dosages of new VMAs and of a superplasticizer (SP) to study the influence on rheology, consistency and washout mass loss. A commercial VMA designated in this paper as “COM” was tested for comparison. The study on new VMAs is encouraging and confirms that pastes with satisfactory rheological and consistency properties comparable with or even better than commercial VMA can be developed. The combined use of proper dosages of VMA and SP is shown to clearly contribute to securing high-performance cement pastes that is highly fluid yet cohesive enough to reduce water dilution and enhance water retention. Attempt has also been made to correlate rheological properties (yield stress) to consistency (slump) of pastes.

Autogenous shrinkage in high-performance cement paste: An evaluation of basic mechanisms

In this paper, various mechanisms suggested to cause autogenous shrinkage are presented. The mechanisms are evaluated from the point of view of their soundness and applicability to quantitative modeling of autogenous shrinkage. The capillary tension approach is advantageous, because it has a sound mechanical and thermodynamical basis. Furthermore, this mechanism is easily applicable in a numerical model when dealing with a continuously changing microstructure. In order to test the numerical model, autogenous deformation and internal relative humidity (RH) of a Portland cement paste were measured during the first week of hardening. The isothermal heat evolution was also recorded to monitor the progress of hydration and the elastic modulus in compression was measured. RH change, degree of hydration and elastic modulus were used as input data for the calculation of autogenous deformation based on the capillary tension approach. Because a part of the RH drop in the cement paste is due to dissolved salts in the pore solution, a method is suggested to separate this effect from self-desiccation and to calculate the actual stress in the pore fluid associated with menisci formation.