Cement Paste Mixes Research Articles

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.

Response Surface Methodology to optimize the cement paste mix design: Time-dependent contribution of fly ash and nano-iron oxide as admixtures

Abstract Response Surface Methodology with a three factor, two level (2 3 ) face centered, central composite design showed that the optimum paste mix design with the water-to-binder at 36.0%, fly ash (FA)-to-binder at 29.5% and nano-iron oxide (NI)-to-binder at 0.78% produced a spread percentage of the fresh paste at 107.0% and, at the same time, compressive strengths of the hardened paste at 22.1, 60.4 and 79.8 MPa after 3, 28 and 90 days of curing, respectively. FA began to play a significant role for the compressive strength after 28 days of curing, whereas NI did after 90 days of curing, indicative of time-dependent contribution of FA and NI to the development of compressive strength. These were further supported by the SEM microstructure analysis. Such a delayed involvement of FA and NI in the cement chemistry should be taken into consideration with care when translating laboratory research results typically based on a 28-day strength to field practice where a shorter curing is typically provided for cost reasons.

Ultrasonic monitoring of the setting of cement-based materials: Frequency dependence

The microstructure of cement-based materials evolves during cement hydration. The foundation of the microstructure is laid during the setting period of concrete. This study experimentally monitors the evolving microstructure network of very early-age cement paste during the setting period. The ultrasonic wave reflection method was applied to probe paste samples, which allows us to obtain the frequency dependence of mechanical impedance. The frequency dependence is due to the development of a pore network and hence inversely describes the initial setting of concrete. A total of 11 cement paste mixes were prepared a different water-to-cement ratios and with the use of various admixtures. Finally, the critical time of frequency-dependent impedance is compared with the initial setting time measured by a Vicat needle test, and the results are discussed with the length of pore path.

Investigation of Thermal Properties of Cement Paste with Fluorescent Lamp Glass Waste, Glass Cullet and Coal/Wood Ashes

The thermal character of cement hydration reactions causes concrete to endure temperature changes during the first days after casting. The present research intends to evaluate the influence on the temperature of hydration of cement paste mixes with local industrial wastes such as lamp glass waste powder/suspension, glass cullet, bottom/fly coal/wood ashes substitution at level of 20% and 30%. The temperature of hydration of cement paste mixes was investigated by using specially designed equipment. The temperature of hydration inside of the cement paste specimens was continuously monitored at least up to 20 h after production at ambient air temperature 20±2°C. The results showed that cement paste substitution with lamp glass waste and coal/wood bottom ashes at level of 30% has influence on the peak temperatures of hydration with decrease from 58.8°C to 46.3°C and cement paste substitution with flint glass at level of 20% decrease temperature of hydration for around 19°C in comparison to control cement paste mix. DOI: http://dx.doi.org/10.5755/j01.sace.2.3.2781

Study on the effects of white rice husk ash and fibrous materials additions on some properties of fiber–cement composites

This work assesses the effects of white rice husk ash (WRHA) as pozzolanic material, virgin kraft pulp (VKP), old corrugated container (OCC) and fibers derived from fiberboard (FFB) as reinforcing agents on some properties of blended cement composites. In the sample preparation, composites were manufactured using fiber-to-cement ratio of 25:75 by weight and 5% CaCl2 as accelerator. Type II Portland cement was replaced by WRHA at 0%, 25% and 50% by weight of binder. A water-to-binder ratio of 0.55 was used for all blended cement paste mixes. For parametric study, compressive strength, water absorption and density of the composite samples were evaluated. Results showed that WRHA can be applied as a pozzolanic material to cement and also improved resistance to water absorption. However, increasing the replacement level of WRHA tends to reduce the compressive strength due to the low binding ability. The optimum replacement level of WRHA in mortar was 25% by weight of binder; this replacement percentage resulted in better compressive strengths and water absorption. OCC fiber is shown to be superior to VKF and FFB fibers in increasing the compressive strength, due to its superior strength properties. As expected, the increase of the WRHA content induced the reduction of bulk density of the cement composites. Statistical analysis showed that the interaction of above-mentioned variable parameters was significant on the mechanical and physical properties at 1% confidence level.

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.

Effect of Palm Oil Fuel Ash Fineness on Packing Effect and Pozzolanic Reaction of Blended Cement Paste

This paper presents the effect of particle size of palm oil ash on packing effect and pozzolanic reaction in cement paste. Ground palm oil fuel ash and ground river sand, having high crystalline and insoluble material of 2 different size with median particle size 15±1 and 2±1μm. Portland cement type I was replaced by palm oil fuel ash or ground river sand at 10, 20, 30 and 40 by weight of cementitious materials. The water to binder ratio (W/B) of 0.35 was used for all the blended cement paste mixes. Compressive strength of cement paste, percentage compressive strength due to hydration reaction, percentage compressive strength due to packing effect, percentage compressive strength due to pozzolanic reaction and fractured surface of cement paste were determined. The results showed that the packing effect of palm oil fuel ash cement paste increases with high fineness. Percentage pozzolanic reaction with median particle size smaller than cement was 12-23% at the age of 28 days. Palm oil fuel ash high fineness is good pozzolanic material and it can be used replace Portland cement Type I at the rate of 30% by weight of binder.

Homogenization Model Examining the Effect of Nanosilica on Concrete Strength and Stiffness

Composite homogenization is a numerical simulation method that allows determination of the effect of microstructure constituents on the mechanical properties of composite materials. This homogenization technique allows cement paste to be modeled as a composite material in which microparticles are randomly dispersed in the cement paste matrix. By using microstructural homogenization, a representative volume element (RVE) can be developed and used to simulate the constitutive model of the composite cement paste by considering its constituent phases. A four-phase cement paste model is considered to describe cement paste incorporating nanosilica. Cement paste microstructures are divided into Phase I, hydrated cement paste; Phase II, unhydrated cement paste; Phase III, nonreacted nanosilica; and Phase IV, capillary porosity. Cement hydration models are used to predict the volume fraction of the four phases on the basis of the mixture proportion of the cement paste mix. Constitutive models for Phases I, III, and IV are assumed on the basis the literature. A constitutive model for Phase II is identified with the RVE model by matching the stress–strain curves of the cement paste extracted from nanoindentation experiments. The validated RVE model is then used to examine the effect of changing the nanosilica content in the cement paste on the stress–strain curve of the composite cement paste. It is evident computationally that increasing the nanosilica content will increase the strength and stiffness of the cement paste and therefore will increase the ability of the cement paste to absorb energy represented by the area under the stress–strain curve.

Influence of clays on the rheology of cement pastes

The fresh state of concrete is becoming increasingly important in furthering the types of applications of today's construction world. Processing techniques have resulted in technologies such as self-consolidating concrete and depend on the microstructural changes that take place during and immediately after mixing and placing. These changes to the microstructure reflect the flocculation behavior between the particles in suspension. The ability to modify this behavior allows control over the balance among flowability and shape-stability of concrete. This study investigates how clay admixtures affect the microstructure of cement pastes from a rheological stand point. Shear and compressive rheology techniques are used to measure how the solids volume fraction of suspensions with different admixtures evolves with stress. Based on these relationships, the effectiveness of clays on the balance between flowability and shape-stability is measured. Results are consistent with green strength tests performed on concrete mixes derived from the cement paste mixes.

Study on the reaction degree of calcined coal gangue powder in blended cement by selective solution method

Calcined coal gangue powder was used to partially replace Portland cement (PC) at 10%, 20%, 30%, and 40% by weight. The water to binder ratio (w/b) of 0.5 was used for all the blended cement paste mixes. The reaction degree of calcined coal gangue powder in calcined coal gangue powder/cement (AC) was determined using a selective dissolution method. It was found that high-volume calcined coal gangue powder pastes underwent a lower degree of reaction of calcined coal gangue powder. The effect of calcined coal gangue powder replacement on the reaction degree of calcined coal gangue powder in AC pastes in later age was less than that of in early age.

The effect of Persian Gulf tidal zone exposure on durability of mixes containing silica fume and blast furnace slag

In this research the performance of cement paste and concrete mixes incorporating 7% and 10% of silica fume (SF) as a cement replacement was investigated in three exposure conditions. The results showed that plain type II portland cement performed better than blended SF cement under cyclic wetting and drying conditions. Silica fume specimens under cyclic wetting and drying conditions in simulated seawater exhibited higher strength loss compared to plain type II portland cement where cured under potable water. In addition, the greater the silica fume amount used in the mixes, the more the capillary water absorption under tidal zone exposure or/and under wetting and drying simulation. Further, the ternary blended ground granulated blast furnace slag (GGBS) mix was the worst performing mix in all exposure conditions.

Effect of coal gangue with different kaolin contents on compressive strength and pore size of blended cement paste

The effects of activated coal gangue on compressive strength, porosity and pore size distribution of hardened cement pastes were investigated. Activated coal gangue with two different kaolin contents, one higher and one lower, were used to partially replace Portland cement at 0%, 10%, and 30% by weight. The water to binder ratio(w/b) of 0.5 was used for all the blended cement paste mixes. Experimental results indicate that the blended cement of activated coal gangue mortar with higher kaolin mineral content has a higher compressive strength than that with lower kaolin mineral content. The porosity and pore size of blended cement mortar were significantly affected by the replacement of activated coal gangue.

Durability of silica fume and ggbs concrete in a tidal zone

This paper summarises investigations that were conducted to assess the durability of plain and blended type II Portland cement exposed to marine tidal environments. In this research the performance of cement paste and concrete mixes incorporating 7 and 10% silica fume as a cement replacement was investigated in three exposure conditions with seven days’ initial curing in potable water. The performance of plain and blended cements was evaluated by monitoring changes in compressive strength and capillary absorption. The results show that plain type II Portland cement performed better than blended silica fume cement under cyclic wetting and drying conditions. Silica fume specimens under cyclic wetting and drying conditions in simulated seawater exhibited higher strength loss in comparison with plain type II Portland cement when cured under potable water. In addition, the greater the silica fume amount used in the mixes, the more the capillary water absorption under tidal zone exposure and/or under wetting and drying simulation. Further, the ternary-blended ground granulated blast-furnace slag mix was the worst-performing mix in all exposure conditions. An extended initial curing time is recommended for these types of mixes.

Effect of fly ash fineness on compressive strength and pore size of blended cement paste

Abstract This paper presents an experimental investigation on the effect of fly ash fineness on compressive strength, porosity, and pore size distribution of hardened cement pastes. Class F fly ash with two fineness, an original fly ash and a classified fly ash, with median particle size of 19.1 and 6.4 μm respectively were used to partially replace portland cement at 0%, 20%, and 40% by weight. The water to binder ratio (w/b) of 0.35 was used for all the blended cement paste mixes. Test results indicated that the blended cement paste with classified fly ash produced paste with higher compressive strength than that with original fly ash. The porosity and pore size of blended cement paste was significantly affected by the replacement of fly ash and its fineness. The replacement of portland cement by original fly ash increased the porosity but decreased the average pore size of the paste. The measured gel porosity (5.7–10 nm) increased with an increase in the fly ash content. The incorporation of classified fly ash decreased the porosity and average pore size of the paste as compared to that with ordinary fly ash. The total porosity and capillary pores decreased while the gel pore increased as a result of the addition of finer fly ash at all replacement levels.

Observations of ice lens formation and frost heave in young Portland cement paste

As part of a research program to image frozen cement past specimens, abnormal microstructural formations are seen in specimens frozen after 10-h hydration. The formations are areas of loose microstructure with aspect ratios of 6–10, which appear perpendicular to the direction of cooling in the specimen. After sublimation of the water in the specimens during the imaging process, these formations collapse, indicating that ice is instrumental to their structure. These formations coincide with longitudinal cracks in the specimen, which do not appear to be due to specimen preparation and are consistent with an internal tensile strain. The authors have hypothesized that ice lens formation and frost heave, or a similar freezing mechanism, is responsible for these microstructural features, which are seen in 10-h specimens and are absent in all other cement paste specimens. Triaxial permeability tests have also shown that the cement paste mix used in this study has a permeability at 10-h age of ∼10 −6 cm/s. This permeability is similar to that of silty soil, some of the most susceptible to frost heave.

Cement-based materials containing shredded scrap truck tyre rubber

Cement paste, mortar, and concrete (containing opc or opc and pfa) mixes were prepared using various proportions of either rubber crumb or low-grade rubber obtained from shredding scrap tyres. Properties examined for the 32 mixes prepared included density, compressive strength, impact and fire resistances, and nailability. Results showed that density and compressive strength of various mixes were reduced by the addition of rubber. (Rubber type had only marginal effect.) Density varied between about 1300 and 2300 kg/m 3. Compressive strength reduced by 70% when the proportion of rubber to total solid content by mass of concrete reached about 13%.

Pore structure of hardened cement paste and mortar

The paper describes an experimental investigation into the pore structure of hardened cement paste and mortar. The pore structure was studied using mercury porosimeter. Ordinary portland cement and natural river sand were used. Pore structure determination was carried out for both the cement paste and mortar mixes over four hydration periods and five water-cement ratios. The threshold radius which was found to be prominent in the hardened cement paste, flattens out as the fine aggregate content increased.

Assessment of the elastic moduli of cement paste and mortar phases in concrete from pulse velocity tests

This paper describes a method for estimating the elastic moduli of the cement paste, mortar and ‘coarse aggregate-paste mixture’ phases in concrete. It is concluded that the elastic moduli of these phases can be predicted without recourse to tests on neat mortar and cement paste mixes. The elastic modulus of a mortar phase in concrete can be significantly different from that of a ‘neat mortar’ having the same mix proportions. Factors such as age, mix proportions and aggregate types, influence the elastic moduli of the different phases.