Cement Paste Mixes Research Articles

Creep and fracture of UHSC — A microindentation study

Creep and fracture behaviour of normal strength concrete was investigated by various researchers whereas, research on creep and fracture of Ultra-High-Strength Concrete (UHSC), i.e., concrete with 28-day compressive strength greater than 100MPa is scanty. Also, a detailed investigation of the creep–fracture interaction of UHSC has not been conducted.This study aims at examining creep and fracture of UHSC cement paste mixes (w/b = 0.20) with varying levels of silica fume (SF) replacement (0%, 20%, and 40%) at different ages (3d, 7d, 28d, 90d) using microindentation technique. Two different holding durations, namely 5 s and 180 s, were considered in the indentation test. The findings revealed a noteworthy variation in estimated fracture toughness (Kc) between the two dwelling periods. Longer sustained loading times (180s) indicated a decrease in fracture toughness for all ages considered, suggesting progressive internal cracking during creep phase. Attempt has been made to investigate the interaction effect.

New insights into early-stage time-dependent dielectric characteristics coupled with frequency dependency and hydration-driven reaction of hydraulic cement pastes: Experiments and statistical modelling

In the field of cement and concrete materials engineering, a comprehensive understanding of dielectric properties is crucial for optimising hydraulic cement paste mix designs. This study examines the relationships among the dielectric constant (ε’), loss tangent (tan δ), frequency, hydration time, water content and admixture dosage in different compositions of hydraulic cement paste. A consistent pattern can be observed across the frequency spectrum, where dielectric constants decrease as frequency increases. This aligns with the expected behaviour of cementitious materials. The most notable finding is the inversely proportional relationship between the loss tangent and frequency. As the frequency increases, the loss tangent consistently decreases, indicating improved energy retention and reduced dissipation. This characteristic is of significant value for various applications, including sustainable infrastructure and smart materials. Furthermore, the interactions among hydration time, water content and admixture dosage present an opportunity for dynamic optimisation within the cement paste matrix. These factors collectively impact dielectric properties, providing insights into the potential for tailored material performance and durability, especially in applications where dielectric properties are critical, such as sensing applications and structural health monitoring of concrete structures. This study emphasises the importance of customising cementitious compositions for specific applications in cement and concrete materials engineering. It achieves this through a detailed comparative analysis of different compositions, each representing varying water content and admixture dosage levels. This approach has the potential to significantly transform the field by enabling engineers to create hydraulic cement pastes with customised dielectric properties that meet the specific requirements of construction, infrastructure and other related applications.

Development of high-volume steel slag as cementitious material by ethylenediamine tetraacetic acid induced accelerated carbonation

Steel slag, a by-product of primary steel production, is produced in large quantities and is primarily used as landfill or aggregate. Due to its high reactivity with CO2, steel slag can form calcium carbonate at room temperature and pressure, making it an ideal material for CO2 capture in the development of sustainable construction materials. Due to the transport properties of CO2 and carbonation kinetics, carbonation of steel slag is frequently carried out using pure gas under high pressure. In this study, ethylenediamine tetraacetic acid (EDTA)-induced accelerated carbonation was used to produce cement paste mixes consisting of up to 100% steel slag powder. Combination of cement and EDTA with steel slag proved to be effective in accelerating the carbonation reaction. EDTA increased the leaching of Ca from the steel slag, thereby enhancing the carbonation reaction, which was more obvious in longer durations (up to 28 days). The optimum cement paste mix (80% steel slag and 20% cement, with 0.1 mol/L EDTA solution) achieved maximum compressive strength of 14 MPa and CO2 uptake of 8.7% after 28 days of accelerated carbonation. Results demonstrated that the use of high-volume steel slag as a cementitious material has great potential in non-structural building applications.

Hybrid effect of GNPs, GOs, and CNTs on the flexural and compressive strengths of cement paste

This paper presents the individual and synergic effects of Graphene Nanoplatelets (GNPs), Graphene Oxides (GOs) and Carbon Nanotubes (CNTs) on the flexural and compressive strengths of cement paste. Mixes containing several nanoparticle types and weight fractions were prepared with Polycarboxylate ether (PCE) surfactant and tested after 90 days of curing. After that, the microstructure of the failed samples was studied using a Scanning Electron Microscope (SEM). Response Surface Methodologies (RSM) techniques were then employed to determine the strength functions' response to the nanofilaments' types and weight fractions. Finally, a cost analysis was done to evaluate the mixes' performance in-terms of strength and cost. Test results showed that the flexural strength of cement paste could be enhanced by 57.33% when using 0.04 wt % GOs. The results also showed that mixes containing 0.08 wt % GOs and 0.12 wt % CNTs improved the flexural strength by 47.03 and 44.38%, respectively when compared with the control cement paste mix. In-terms of compressive strength, mixes containing 0.04 wt % GNPs attained the highest compressive strength improvement of 15.7% when compared with the control mix. In hybrid mixes containing more than one nanoparticle type, the best synergistic action was generated between 50% CNTs and 50% GOs at a total dosage of 0.04% wt, where the compressive strength increased by 20.2%. The microstructural analysis showed good dispersion qualities and nanoparticles embedment within cement hydration products. On the other hand, RSM analysis showed that the maximum compressive and flexural strength functions' responses are obtained at the lowest nanofilaments’ weight fraction of 0.04 wt %. The desirability analysis confirmed that the compressive and flexural strengths of cement paste could be improved by 7 and 53%, respectively, using the predicted formulas. Finally, the cost analysis showed that GO-modified cement pastes are considerably more expensive than other mixes, yielding the lowest economic index.

β-CaSiO3 and colloidal n-SiO2 based blended cement composites- their properties, regression analysis and micro-characterization studies

This paper examines the effect on mechanical properties such as compressive strength, flexural strength, and dynamic modulus of elasticity (DYE) of different proportions of wollastonite (β-CaSiO3) and colloidal nano-silica (n-SiO2) partially replacing cement. Durability indicators (water absorption, sorptivity and sulphate treatment test) were also examined to ascertain the quality of hardened paste mixes with respect to the control mix. The regression models were found for mechanical properties using different parameters from the results obtained, and statistical relations were established and validated. Regression analysis shows the significance of every parameter considered and model for the prediction of mechanical strengths. Finally, the results were substantiated by the microstructural characterization by FESEM. β-CaSiO3 and colloidal n-SiO2 replaced cement by 15%, and 1.5%-6% with an offset of 1.5%, respectively at low (0.25), medium (0.40) and high (0.55) water/binder (w/b) ratio. FESEM micrographs showed dense Calcium-silicate-hydrate (CSH) gel and stratlingite (CASH) was formed by blended cement paste mixes containing β-CaSiO3 and n-SiO2. n-SiO2 at 3% and CaSiO3 at 15% replacements of cement (NS3 mix) was the optimum replacement level for the cement paste mix. Analysed regression model suggests that the models and parameters were found significant and can also be used for prediction (based on R2 values and p-value).

ポリマーセメントペーストを用いたシート防水密着構法に関する研究（その１）：ポリマーセメントペーストの調合が接着性および水密性に及ぼす影響

In this paper, two experiments were conducted to clarify the influence of polymer cement paste mix proportion on in-plane permeability resistance, adhesiveness and watertightness. The followings are concluded from the test results. If the quality of the underlying concrete is poor, fracture at the interface between substrate and hardened paste is likely to occur. If the paste is a softer mix proportion, adhesive failure and moisture migration are more likely to occur due to the formation of a fragile layer, presumably caused by bleeding. These problems can be improved by mixing a standard amount of polymer in this waterproofing system.

Probability Characteristics of a Crack Hitting Spherical Healing Agent Particles: Application to a Self-Healing Cementitious System.

A geometric model is developed to statistically study the probability characteristics of crack intersecting self-healing capsules with a structured random distribution in a cement paste mix. To evaluate the probability of a crack intersecting encapsulated particles, the fill ratio of the crack, and the depth of the first-hit capsule, Monte Carlo simulations are performed. The variables are the crack geometry, i.e., width, length, depth, orientation, skewness, and so on; the size and mass fraction of healing capsules; and the agglomeration of capsules. Models based on statistical analyses for hit probability , crack fill ratio at 95% confidence level, and first hit depth at 95% confidence level are expressed as functions of capsule size and mass fraction, as well as crack geometry. The model assumptions and results are evaluated using data reported in the literature. The data include results from experimental and theoretical studies.

Compatibility of superplasticizers with cement paste and concrete mixes containing Type I and Type V cement, and volcanic ash

Compatibility of superplasticizers with cement paste and concrete mixes containing Type I and Type V cement, and volcanic ash

Cement Paste Mixture Proportioning with Particle Packing Theory: An Ambiguous Effect of Microsilica

Recently, the research of innovative building materials is focused on applying supplementary materials in the form of micro- and nanopowders in cementitious composites due to the growing insistence on sustainable development. Considering above, in paper, a research on the effect of microsilica and SiO2 nanoparticles addition to cement paste, designed with Andreasen and Andersen (AA) packing density model (PDM), in terms of its physical and mechanical properties was conducted. Density, porosity, compressive strength, hardness, and modulus of indentation were investigated and compared regarding different amount of additives used in cement paste mixes. Microstructure of the obtained pastes was analyzed. The possibility of negative influence of alkali-silica reaction (ASR) on the mechanical properties of the obtained composites was analyzed. The results of the conducted investigations were discussed, and conclusions, also practical, were presented. The obtained results confirmed that the applied PDM may be an effective tool in cement paste design, when low porosity of prepared composite is required. On the other hand, the application of AA model did not bring satisfactory results of mechanical performance as expected, what was related, as shown by SEM imaging, with inhomogeneous dispersion of microsilica, and creation of agglomerates acting as reactive aggregates, what as a consequence caused ASR reaction, crack occurrence and lowered mechanical properties. Finally, the study found that the use of about 7.5% wt. of microsilica is the optimum in regards to obtain low porosity, while, to achieve improved mechanical properties, the use of 4 wt. % of microsilica seems to be optimal, in the case of tested cement pastes.

Quantitative Measurement of Water Absorption of Coarse Lightweight Aggregates in Freshly-Mixed Concrete

The high water-absorption of lightweight aggregate causes a high slump loss and poor workability of concrete. A prewetting process is usually recommended to compensate for the workability problem, but its application needs more delicate consideration in field. A method is proposed to measure the additional water absorption of lightweight aggregate, and its application in cement paste and concrete mixes confirms the absorption amount remaining unaffected by the mix proportion. The additional water absorption in cement-based materials can be considered as a material property, and its value is smaller than the water absorption measured by a standard test method (water-soaking). Compensating the additional water absorption finally allows to use dry lightweight aggregates for concrete, which is more robust and stabler than taking a saturated surface-dry lightweight aggregates.

A BIO-BASED RHEOLOGY MODIFYING AGENT INSPIRED FROM NATURE


 
 Interaction of microorganisms and building materials, particularly with
 concrete and stone, were a main topic of interest for many researchers.
 Initially, studies focused on degradation of concrete by
 organic acids, produced by microbial acidification such as microbial induced
 corrosion. This was followed by prevention of microorganisms fouling on building
 materials. However, the interaction of microorganisms with materials is not
 necessarily negative. Recent research in the field shows that microorganisms
 can have positive effects on concrete and stone, such as in biological cleaning
 and biocalcification, which resulted with stronger and more durable materials.
 Further, studies revealed that it was possible to develop smart-cement based
 materials that could self-heal microorganisms by leveraging metabolic activity
 of microorganisms. Through the development of this so-called smart bio-based
 mortar, it became possible to improve the fresh state performance of the mix.
 This study focusses on design of a cement-based mortar with improved
 rheological properties with use of Bacillus
 megaterium (B. megaterium) and
 Bacillus subtilis (B. subtilis) cells. The bacterial cells were directly
 incorporated to the mix water and influence of cells on viscosity and yield
 strength was evaluated by rheological tests. In addition, the influence of
 bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly
 ash on performance of biological VMA were investigated. Our results showed that
 the apparent viscosity and yield stress of the cement-paste mix were increased
 with the addition of the microorganisms. Moreover, B. megaterium cells were found to be compatible with both fly ash
 and superplasticizers however B. subtilis
 were only be able to increase the viscosity when they were incorporated with
 superplasticizers.

Thermogravimetric analysis and microstructure of alkali-activated metakaolin cement pastes

This study reports the thermogravimetric analysis and microstructure characteristic of alkali-activated metakaolin cement pastes using Na2SiO3-to-NaOH ratio of 1.5. Metakaolin was used at 70, 80, 90, 95 and 100% by total mass of binder, and Portland cement (ASTM Type I) was used at 0–30% by total mass. Alkali/binder ratio of 1.5 and water curing at 23 °C was used. Thermogravimetric analysis and scanning electron micrographs showed that at 70% metakaolin the major phase found is calcium silicate hydrate (C–S–H) which is normally found in normal water-based cement paste mixes with a slight shoulder peak of N–A–S–H. At higher metakaolin content (80% and higher), sodium aluminium silicate hydrate (N–A–S–H) phase was detected as found in geopolymer, and this is the case in 100% metakaolin mix where essentially only N–A–S–H was found. The compressive strength results were found in the region of 43–48 MPa with higher strength found at higher metakaolin content. Therefore, the results of alkali-activated metakaolin cement paste mixes showed interesting change in the major phase of C–S–H to N–A–S–H depending on amount of Portland cement and metakaolin.

Influence of Sporasarcina pasteurii cells on rheological properties of cement paste

Nowadays with the developments in the concrete materials technology, researches started to focus on highly flowable mixes with improved rheological properties. These highly flowable mixes generally require use of viscosity modifying agents (VMAs) to reduce bleeding and segregation. VMAs are water-soluble polymers that can be produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Through the literature, nopal mucilage, brown algae and bacterial cell walls were proposed as alternatives to these bio-based admixtures. However, these alternatives also require extra processing which results again with a higher unit cost. This paper summarizes the rheological properties of a cement paste including bacterial cells. The main goal of this study was to investigate the influence of Sporasarcina pasteurii (S. pasteurii) cells on viscosity and yield stress of cement-based materials. The bacterial cells were directly incorporated to the mix water and influence of cells on viscosity and yield strength was evaluated by rheological tests. In addition, the influence of bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly ash on performance of biological VMA were investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, the provided biological VMA was found to be compatible with the use of fly ash and superplasticizers depending on the w/c of cement paste.

Gravel wash mud, a quarry waste material as supplementary cementitious material (SCM)

The suitability of gravel wash mud (GWM), a sludge waste from gravel quarrying, is examined for its use as a partial Ordinary Portland cement (OPC) clinker substitute. The gravel wash mud was dried, milled into a fine powder and calcined at 750 °C, 850 °C and 950 °C. In this study, various characterisation methods including particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD) and the simultaneous thermal analysis (STA) were applied on the calcined GWM powders to determine the optimal calcination temperature. Over 200 specimens were prepared based on different cement paste and mortar mixes to investigate the potential of calcined GWM powders as SCMs. The pozzolanic activity of the GWM powders was verified by applying strength-based evaluation methods, simultaneous thermal analysis and SEM on hardened samples. Very promising strength-enhancing capacities were observed for samples containing GWM powders calcined at 850 °C with an OPC replacement level of 20 wt%.

Assessment of parameters governing the steel fiber alignment in fresh cement-based composites

Abstract The main aim of this paper is to measure the induced torque needed to rotate a steel fiber, hence an experimental and parametrical analysis of factors governing steel fiber alignment in cement pastes and mortar, rotating from static position and rotating in a dynamic fluid is here presented. To aim this objective, a set of rheological tests has been conducted to assess the torque necessary to rotate steel fibers immersed into different fresh cement paste and mortar mixes with Bingham fluid behaviour. Fibers of different aspect ratios (length/width) and different geometry, straight and hooked-end, have been evaluated as they are the more commonly used. On the other hand, different parameters (type of mixture, size of aggregates, volume fraction of aggregates) affecting cement mixtures are also analysed and their influence in fiber orientation discussed. Fiber alignment depends on external torques applied to fibers, immersed into a cement-water-aggregate viscous system, that can be produced during or after casting. The flowability of the fresh suspension with fibers produces a load/pressure that generates a torque that can align them. Fiber alignment is a main goal to pump the fresh material. Hence, the factors that govern fiber alignment are studied which increase the post-cracking strength of cement-based composites under load along its life service due to casting or pumping. To that end, a set of tests has been conducted to assess the torque necessary to rotate steel fibers immersed into different fresh cement paste and mortar mixes with Bingham fluid behaviour. Fibers of different aspect ratios(length/width) and different geometry (straight and hooked-end) have been evaluated. On the other hand, different parameters (type of mixture, size of aggregates, volume fraction of aggregates) affecting cement mixtures are also analysed and their influence on fiber orientation is discussed. The values obtained here are between 1 and 14 N · mm of dynamic yield torque and 0.1 and 0.5 N · mm min for viscoplastic torque per fiber, depending on fiber geometry, are helpful to improve the fiber alignment in cement-based composites reinforced with fibers through a design and production based on these parameters.

Relationship Between Air-Content in Fresh Cement Paste, Mortar, Mix and Hardened Concrete Acc. to PN-EN 480-1 with Air-Entraining CEM II/B-V

Research results of the relationships between air-volume in air-entrained cement paste, mortar and concrete, all designed according to PN-EN 480-1 guidelines are presented in the paper. The cement paste, mortar and concrete, with w/c=0,5 ratio, were prepared using innovative air-entraining cement CEM II/B-V. The air-entraining cement CEM II/B-V was produced using two methods: mixed together with natural or synthetic aerated admixture. The air volume test of the volumetric method was carried out in case of fresh cement paste, mortar and concrete mix. Fresh concretes were evaluated in terms of stability of air entrainment and consistency for 5, 20 and 40 min. The porosity structure parameters, like summarized air-content, specific surface of air voids, air-voids spacing factor and micropores content of hardened concrete, were estimated using computer tomography with a resolution of 2-5 μm. The aim of the research was to determine the dependence between air-content of cement paste, mortar and concrete on the measurement of air-entrainment of cement paste or mortar with the same w/c ratio and type of cement, all designed according to PN-EN 480-1 guidelines. Test results proved that there is a good correlation between the measured air-content of the cement paste, mortar and concrete. Therefore, it is possible to predict the aeration of concrete on the air-entrainment of the mortar. Moreover, the porosity parameters research results indicated, that the air-entrainment of concrete is very stable. Research results indicated that the porosity of hardened concrete meets the European standards for frost-resistant concrete. Research results of the influence of air- entraining admixture type have proved, that a greater amount of micro pores in concrete is the effect of a synthetic air-entraining admixture. In concrete with synthetic entraining admixtures the air pores have smaller diameters than in concrete with natural air-entraining admixture, which are being transferred into their specific surface. The synthetic admixture is more recommended than the natural one also because of the value of the air-voids spacing factor of concrete.

Influence of a Retarding Admixture on the Behavior of Mortars Made from Different Types of Cement

The effect of retarding admixture on the fresh and hardened behaviour of different types of cement mortars and pastes when using a retarding admixture was investigated in this study. The types of cement used are; White cement (WhC), Ordinary Portland cement (OPC) and Sulphate Resistant Portland cement (SRC). Different cement mortar and paste mixes were cast, for this purpose, with and without the admixture. Initial and final setting times, compressive strength, length change, absorption and density for these mixes were examined at the curing ages of 3,7,28,45 days. The results showed that the addition of retarding admixture delayed the setting time significantly of WhC paste. The retarding admixture has a positive effect on the compressive strength of the mortar specimens for all types of cement used. regarding the length change test, the admixture was found to reduce the initial expansion for all types of cement at all ages. The results also showed an increase in the density and decrease in water absorption, especially at the later ages for all types of cement. Among all cement types used, WhC was noticeably the most affected type by using the retarding admixture compared to other types of cement used.

Uniaxial confined compression tests of cementitious materials

This paper aims at presenting the development of an experimental setup to perform confined compression tests of mortar and cement paste specimens at high pressures. The paper presents the effect of water/cement ratio (w/c) as well as the ratio of fine aggregate (sand) and its maximum grain size on the measured pressure – volumetric strain dependence (equation of state). Decrease of w/c ratio in a cement paste mix results in increase of the secant bulk modulus of the loading branch. The study includes unloading and reloading at different load levels. The bulk modulus of the reloading branch of a given composition depends almost linearly on the pressure magnitude. The secant bulk modulus (loading branch) of mortar specimens increases monotonically with the volumetric sand fraction. The experimental study shows a good repeatability of the different cement paste specimens and of specimens with fine sand; a relatively large scatter of the results is obtained for specimens with coarse sand. The developed damage was identified and recorded at the end of each test. In cement paste specimens cracks were identified only in the case of w/c=0.50, while in the other specimens, no cracking was observed. In the mortar specimens with coarse sand, perpendicular cracks to the specimen axis were observed, while in the specimens, that contain fine sand, no damage has been indicated.

Behavior of magnetic concrete incorporated with Egyptian nano alumina

This research is the first attempt to determine the possibility of using magnetized water (MW) to improve fresh, mechanical, and microstructure characteristics of concrete incorporated with Egyptian nano alumina (NA). For this purpose, slump, compressive strength, desorption, and scanning electron microscopy (SEM) approaches were conducted. Eight concrete mixes and eight cement paste mixes were made with different NA contents (0, 1, 2, and 3% by weight of OPC). Two types of water, normal tap water (TW) and MW of 1.2Tesla were used. Using MW instead of TW had led to a significant improvement in all considered characteristics of concrete. For non-magnetic concrete (NMC), the use of 1% replacement level of NA improved the properties of concrete. While, for magnetic concrete (MC), there was notable improvements in concrete characteristics of 1% NA and 2% NA specimens compared to control specimen. The proper content of NA to be used in both NMC and MC was 1% by weight of OPC. NMC made with 1% NA showed the highest increase in strength (17%) and decrease in capillary porosity (30%). MC made with 1% NA showed the highest increase in strength in (13%) and decrease in capillary porosity (27%) as compared to control specimen.

On the Equation of State of Cementitious Composites - an Experimental Study

Abstract The behavior of cementitious materials under severe loading is of particular interest, for research on ballistic impact, penetration and near distance explosions, where very high pressures are developed. Therefore it is important to investigate the behavior of such materials in the exceptionally high hydrostatic pressures range. One of the key characteristics of this behavior is the equation of state (EOS) that is the relationship between hydrostatic pressure and density (or bulk strain). However it has not been adequately investigated, and therefore the mechanisms of cementitious materials deformation and damage that are developed within that range of high pressures is at least partly obscure and far from being clearly understood. This is partly because the controlled application of extreme pressures requires special equipment and expensive experimental setups and testing is associated with a wide variety of technical problems. This paper aims at presentation of the development of an experimental setup to perform confined compression tests of mortar and concrete specimens at high pressures up to 1GPa. It presents the experimental study of different cement paste and mortar specimens and their comparison with previous results, obtained under high pressures up to 300 MPa. This allows the investigations of size effect for unsaturated samples, as well as the effect of the sand volumetric content on the loading branch of the equation of state. The experimental study shows a good repeatability for the cement paste specimens and for mortar specimens with fine sand. It also shows that decrease of water/cement ratio in the cement paste mix as well as increase of the sand volumetric contain in mortar results in monotonic increase of the secant bulk modulus of the loading branch of EOS. The comparison of the mean loading branch of the experimental EOS for unsaturated specimens having 30 mm diameter (70 mm height) and 70 mm diameter (150 mm height) clearly indicates that there is practically no size effect for all tested mixture compositions. While for the cement paste there is no difference up to 270 MPa (highest pressure level in the test in the small apparatus), the addition of sand yields an increase of the difference, which, anyway, remains small.