Compressive Strength Of Cement Paste Research Articles

Comparative roles between aragonite and calcite calcium carbonate whiskers in the hydration and strength of cement paste

Aragonite CaCO3 whisker (CW) could improve the mechanical properties of cementitious composites. The microstructure of calcite is different from that of aragonite, but only a few studies reported different effects in cementitious composites between incorporating aragonite and calcite. In order to fully use CW as high-performance, low-cost microfiber and clearly understand different mechanisms between aragonite and calcite CW, in this study, the heat treatment method was used to convert aragonite CW to calcite CW, and the effect of calcite and aragonite on the hydration and strength of CW reinforced cement paste (CWRC) was studied to bridge the gaps in this area. The aragonite and calcite CWs exhibited the overall physical dilution effect in Portland cement, significantly decreasing the hydration heat of cement and the total amount of non-evaporable water and Ca(OH)2. Calcite CW presents a more significant nucleation effect than aragonite CW. Compared to aragonite CWRC, the hydration of silicon phase in calcite CWRC is faster and the hydration heat release is higher; however, there is no significant difference in the hydration of aluminum phase. The Ca(OH)2 content in calcite CWRC was more than that in aragonite CWRC. More hydration products formed on the surface of calcite CW than that on aragonite CW, improving the bonding strength between calcite CW and cement matrix. Hence, both the compressive strength and flexural strength of calcite CWRC are higher than those of aragonite CWRC. The rheological test of fresh aragonite and calcite CWRC proved that both aragonite and calcite CWs significantly decreased the flow of cement paste, presenting viscosity effect. Compared to aragonite CW, calcite CW improved the flowability of fresh cement paste, indicating the lubricant effect of calcite CW. Aragonite and calcite CW present chemical effect similar to limestone powders, i.e., aluminum phase in Portland cement interacted with CO32- dissolved from CW to form mono- and semi- carbonate. The Ca(OH)2 orientation indexes of cement decreased by the introduction of CWs. Aragonite and calcite CWs can also be used as microfiber and filler in cementitious composites. These effects improved the micro-structure, thus enhanced the flexural and compressive strength of cement paste.

Effect of nano-SnO2 on early-age hydration of Portland cement paste

Nanomaterial, as a new emerging material in the field of civil engineering, has been widely utilized to enhance the mechanical properties of cementitious material. Nano-SnO2 has presented high hardness characteristics, but there is little study of the application of nano-SnO2 in the cementitious materials. This study mainly investigated the hydration characteristics and strength development of Portland cement paste incorporating nano-SnO2 powders with 0%, 0.08%, and 0.20% dosage. It was found that the early-age compressive strength of cement paste could be greatly improved when nano-SnO2 was incorporated with 0.08% dosage. The hydration process and microstructure were then measured by hydraulic test machine, calorimeter, nanoindentation, X-ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. It was found that the cement hydration process was promoted by the addition of nano-SnO2, and the total amount of heat released from cement hydration is also increased. In addition, the addition of nano-SnO2 can promote the generations of high density C-S-H and reduce the generations of low density C-S-H indicating the nucleation effect of nano-SnO2 in the crystal growth process. The porosity and probable pore diameter of cement paste with 0.08% nano-SnO2 were decreased, and the scanning electron microscopic results also show that the cement paste with 0.08% nano-SnO2 promotes the densification of cement microstructure, which are consistent with the strength performance.

Effects of pozzolanic and non-pozzolanic nanomaterials on cement-based materials

Although it has been verified that nanomaterials can improve the properties of cement-based materials, the research on the characteristics and mechanism of different types of nanomaterials is still inadequate. Two typical types of nanomaterials, nano-SiO2 (pozzolanic material) and nano-TiO2 (non-pozzolanic material), are utilized in this paper to investigate the combined effects of reactivity, size, and content on the efficiency of nanomaterials in cement-based materials. The experimental results indicate that the size and content effect of nano-SiO2 is obvious. Small size and large content of nano-SiO2 can significantly improve the compressive strength of cement paste. However, the size effect of nano-TiO2 is much weaker than that of nano-SiO2, and the content effect of nano-TiO2 is only obvious at the early age. For the late age compressive strength, the small content of nano-TiO2 shows a similar obviously improving effect as the big content of nano-TiO2. The pore structure analysis shows that both nano-SiO2 and nano-TiO2 can reduce the total porosity of cement paste, but nano-TiO2 is more effective than nano-SiO2 at reducing the harmful pores. Therefore, the small content of nano-TiO2 is more effective to enhance the impermeability of cement-based materials. The results of this paper show that nano-SiO2 and nano-TiO2 have different effects and they should be selected based on the properties requirement of cement-based materials.

Aggregation size effect of graphene oxide on its reinforcing efficiency to cement-based materials

Aggregation of graphene oxide (GO) in cement matrix greatly reduces its reinforcing efficiency to the mechanical properties of cement-based materials. However, current technology is too difficult to distinguish the aggregated GO from the complex components in hardened cement matrix, so how does the GO aggregation influence the mechanical properties of cement-based materials is still not clear. In this study, the aggregation size effect of GO on its reinforcing efficiency to cement-based materials was investigated by pre-aggregating GO in aqueous solutions by a novel extrusion method before mixing with cement particles. It was found that with the increasing aggregation size of GO from nanometers, micrometers to millimeters, its reinforcing efficiency to the compressive strength of cement paste was gradually reduced, because the intrinsic advantages of excellent mechanical properties and high specific surface area of GO faded away with the increasing size of GO. More importantly, the mechanism behind that the addition of GO always showed a stronger mechanical reinforcement to cement mortar than paste was revealed by measuring the particle size variation of aggregated GO in a simulated alkaline cementitious solution with and without sand under mixing process. The sand shearing effect on de-aggregation of GO by reducing their particle size, for the first time, was proposed. Compared with the aggregated GO with a larger size, the de-aggregated GO with a smaller size and larger specific surface area due to the sand shearing effect should be responsible for the stronger mechanical reinforcement to cement mortar. In conclusion, this study provides a new perspective to the GO reinforcing efficiency to the mechanical properties of cement-based materials in terms of aggregation size of GO and sand shearing effect.

The role of admixed graphene oxide in a cement hydration system

Graphene oxide (GO), which has been sucessfully used in cement composites as an admixture, can improve their mechanical and durability properties. This study examined and elucidated the effect of GO on the hydration products of a cement system in detail. The hydration precursors, morphology, composition, and chemical bonds of cement pastes were studied by SEM/BSE, XRD, LA-ICP-MS, and 29Si/27Al MAS-NMR, respectively. The experimental results indicated that the 28-day compressive strength of cement pastes (w/c = 0.35) was increased by 29% when admixing 0.02 wt% GO. There existed chemical reactions between the admixed GO and the cement hydration products. The improved strength actually was not only attributed to the improved hydration degree of cement, but also the newly found tobermorite-like hydrates and jennite-like hydrates due to the Ca ions consumption by the negatively charged GO. The polymerization of hydration products was also improved due to the addition of GO.

A quantitative study on physical and chemical effects of limestone powder on properties of cement pastes

The study aims to quantitatively calculate the physical and chemical effects of limestone powder (LP) with four average particle sizes and two amounts in cement pastes by using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) techniques. At 3d, as the average particle size of LP decreased from 32 to 6 μm, the consumed CaCO3 content in LP increased from 0.67% to 1.71%, and the chemically reactive portion of LP increased from 1.15% to 2.95%. However, at 180d, the consumed CaCO3 content and chemically reactive portion of LP was almost 2.4% and 4.2%, respectively. At 3d, as the LP content increased from 25% to 50%, the consumed CaCO3 content in LP increased from 1.71% to 2.02%, and the chemically reactive portion of LP increased from 2.95% to 3.5%. However, at 180d, the differences of consumed CaCO3 content and chemically reactive portion of LP between cement pastes with different LP content were limited. The physical and chemical effects of limestone powder on the compressive strength of cement pastes were calculated. At 180d, as the average particle size of LP decreased from 32 to 6 μm, the contribution of chemical effect of LP on the compressive strength of cement pastes increased from 1.01% to 1.08% while the contribution of physical effect decreased from 21.19% to 20.03%.

Novel bifunctional dispersing agents from waste PET packaging materials and interaction with cement

Modified polyethylene terephthalate polymers (MPETs), as a novel dispersing agent, were successfully prepared from polyethylene terephthalate (PET (flakes of empty bottles in order to recycle waste from one particularly abundance packaging material. Different techniques were used to characterize the MPETs samples, including attenuated total reflectance Fourier transform infrared (ATR-FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), scanning electron microscope (SEM), dynamic light scattering (DLS) and Brunauer–Emmett–Teller (BET) surface area. The fluidity and mini-slump retention of fresh cement paste were tested to evaluate the dispersion capability of the MPETs. The effect of MPETs on the setting time and compressive strength of the cement paste were studied. The adsorptive behavior of the MPETs dispersions was examined using total organic carbon (TOC) and zeta potential to interpret the interaction of the MPETs with cement. The results show that the MPETs can be adsorbed on the cement particles and improve the flowability, setting time and the compressive strength of cement paste. Adding value by generating a cheap and effective dispersing agent from recycling waste polymers is a great approach toward eco-friendly waste management.

Upcycling carbon dioxide to improve mechanical strength of Portland cement

Abstract To reduce environmental pollution induced by the production of Portland cement and sequestrate greenhouse gas, a novel approach was developed to manufacture nano-calcium carbonate (nano-CaCO3) suspension by upcycling carbon dioxide. The influence of this nano-CaCO3 suspension on basic performances of Portland cement paste was experimentally evaluated and related mechanisms were demonstrated by isothermal heat conduction calorimeter (TAM Air), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimeter (MIP), scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements. Experimental results showed that the manufactured CaCO3 presented spherical and cubic shapes with size of 20–50 nm. This CO2 upcycling method can improve compressive strength of cement paste by 5.8–9.9% at ages of 3–56 days and significantly reduce the initial and final setting times. The introduction of CO2 in form of nano-CaCO3 accelerated the early age hydration of Portland cement and refined the pore structure. Around 0.4–2.4 kg of CO2 can be recycled by every ton of Portland cement while the usage efficiency of cement was evidently improved. Therefore, both capture and solidification of carbon dioxide and carbon footprint reduction of cement industry can be simultaneously achieved by this technology.

Microstructural Properties of Cement Paste and Mortar Modified by Low Cost Nanoplatelets Sourced from Natural Materials.

Nanomaterials have been widely used in cement-based materials. Graphene has excellent properties for improving the durability of cement-based materials. Given its high production budget, it has limited its wide potential for application in the field of engineering. Hence, it is very meaningful to obtain low cost nanoplatelets from natural materials that can replace graphene nanoplatelets (GNPs) The purpose of this paper is to improve the resistance to chloride ion penetration by optimizing the pore structure of cement-based materials, and another point is to reduce investment costs. The results illustrated that low cost CaCO3 nanoplatelets (CCNPs) were successfully obtained under alkali treatment of seashell powder, and the chloride ion permeability of cement-based materials significantly decreased by 15.7% compared to that of the control samples when CCNPs were incorporated. Furthermore, the compressive strength of cement pastes at the age of 28 days increased by 37.9% than that of the plain sample. Improvement of performance of cement-based materials can be partly attributed to the refinement of the pore structure. In addition, AFM was employed to characterize the nanoplatelet thickness of CCNPs and the pore structures of the cement-based composites were analyzed by MIP, respectively. CCNPs composite cement best performance could lay the foundation for further study of the durability of cement-based materials and the application of decontaminated seashells.

Evaluation the compressive strength of the cement paste blended with supplementary cementitious materials using a piezoelectric-based sensor

This paper aims to investigate the feasibility of using piezoelectric-based sensors to characterize the compressive strength gain process of cement paste blended with supplementary cementitious materials. The electromechanical impedance technique was used for in-situ monitoring of the strength gain of cement pastes. Two different indices of root mean square deviation (RMSD) and correlation coefficient (CC) have been used to establish a quantitative correlation between the conductance signature obtained by lead zirconate titanate (PZT) sensors and the compressive strength of cement paste. Both indices exhibited a reasonable qualitative trend which was compatible with the trend of strength gain of cement pastes. However, the RMSD was found to be more efficient than CC index in estimating the compressive strength of cement paste over time. The experimental results indicate that EMI can be used as a nondestructive testing (NDT) method to enable in-situ measurement of strength gain process of cement paste with supplementary cementitious materials.

Role of layered double hydroxides in setting, hydration degree, microstructure and compressive strength of cement paste

Abstract The effects of calcined Mg-Al-CO3 LDH on setting time, hydration degree, microstructure as well as compressive strength of cement pastes were explored. Furthermore, the role of LDH in cement system has been revealed by characterizing the component and structural changes of LDH. The experimental results show that LDH is physically and chemically active in cement paste. 1–3% calcined LDH accelerates the hardening process and improve the setting of cement to some extent. LDH incorporation leads to the slight increasing in non evaporable water content, and the increasing ratio is less than 1% at each curing age. The hydration heat for LDH blended specimens are less than that of control cement because of the dilution effect. LDH accelerates the hydration reaction to some extent even though it is not a dramatic change. LDH has refine effect on pore structure of cement paste and the addition level of LDH should be no less than 2%. Cement pastes with LDH exhibits increased compressive strength regardless of curing time, and the increase rate at 28 days is lower than that obtained at early ages. Fulfillment of structure regeneration of calcined LDH in cement paste environment was also been revealed.

Effects of SCMs particles on the compressive strength of micro-structurally designed cement paste: Inherent characteristic effect, particle size refinement effect, and hydration effect

To clarify the effects of supplementary cementitious materials (SCMs) on the mechanical properties of cement-based materials, micro-structurally designed cement pastes, which were prepared by adding mono-sized SCMs into ultrafine Portland cement, were subjected to compressive strength tests. By changing the type, the addition and the size of SCMs in the micro-structurally designed cement pastes, effects of SCMs particles on the compressive strengths of cement pastes were quantitatively characterized, and then classified into inherent characteristic effect, particle size refinement effect, and hydration effect. Specifically, compressive strengths related to inherent characteristic effects of clinker, granulated blast furnace slag (GBFS), fly ash (FA) and quartz sand (QS) were 50.8 MPa, 44.6 MPa, 39.6 MPa, and 36.0 MPa, respectively. In contrast, compressive strength related to particle size refinement effect increased to 4.2 MPa when the D50 of SCMs decreased to 2.4 μm. Compressive strengths related to hydration effect of clinker, GBFS, and FA can be as high as 30.8 MPa, 22.5 MPa, and 9.1 MPa, respectively. Finally, an empirical model was established and validated to predict the compressive strength of cement paste with SCMs. The results will give a better understanding on rational utilization of SCMs or inert fillers to prepare cement-based materials with qualified mechanical properties and durability.

Влияние oксида графена на прочность при сжатии цементного камня

Влияние oксида графена на прочность при сжатии цементного камня

Influence of elevated curing temperature on the properties of cement paste and concrete at the same hydration degree

Three different curing temperatures (20 °C, 40 °C, and 60 °C) were set, so that the nonevaporable water (wn) contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree (wn=15%) or high hydration degree (wn=16.5%), elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore (>100 nm) volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste’s compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.

The Behevior of Lauryl glucoside as cement paste admixture

The use of air entraining agents have been accepted practice in cement technology for many years. A large number of uniform and stable micro bubbles is intentionally entrained to improve the durability and reduce the potential for damage from freezing and thawing, but these bubbles are inversely affected the hardened cement paste compressive strength. The Physiochemical and Mechanical Properties of cement pastes containing synthetic nonionic surfactant Lauryl glucoside (LG) as air-entraining agents are investigated. Different cement pastes with and without LG are prepared for five interval times (3, 7, 28, 90 and 360 days). The influence of the different surfactant concentrations on the air content of the pastes and accordingly the bulk density, compressive strength and microstructure of the hardened cement specimens is discussed. The optimal level of factors to achieve the desired goals are determined. The results show that LG causes a uniform distribution of small air voids in the cement paste, beside its ability to accelerate the hydration reaction, which may greatly improve the compressive strength of the pastes.

Optimum carbon nanotubes’ content for improving flexural and compressive strength of cement paste

This study investigated the effect of multi-walled carbon nanotubes’ (MWCNTs) weight fraction on the setting time and mechanical properties of cementitious composites. Different cement mixes containing CNT-to-cement weight fractions of 0.03, 0.08, 0.15, 0.25, 0.35 and 0.5wt% were prepared in addition to the control mix. The initial and final setting times of the fresh pastes were measured on the cast day and the flexural and compressive strengths of the hardened samples were determined after 28days of moist curing. The fractured surfaces of the samples were then examined using a scanning electron microscope (SEM). The results showed that the 0.25wt% CNTs is the optimum weight fraction in terms of achieving maximum strength at a reasonable cost. Batches with lower CNTs’ contents than 0.25wt% demonstrated lower flexural and compressive strengths, whereas batches with higher CNTs’ contents than 0.25wt% produced similar or slightly higher strengths. Analysis of variance (ANOVA) confirmed that increasing CNTs’ concentration above 0.25wt% will not have a significant effect on the compressive and flexural strengths. Investigations of the microstructure, which was carried out using SEM, showed good dispersions of the nanofilaments within the cement matrix. Spots of agglomerations were noticed in batches containing 0.25, 0.35 and 0.5wt%. SEM images have also indicated that CNTs were embedded within the cement hydration products. The study findings were useful for determining the CNTs’ content required to achieve both optimum dispersion and maximum strength enhancement of cementitious composites.

Effects of graphene oxide agglomerates on workability, hydration, microstructure and compressive strength of cement paste

In this study, the effects of graphene oxide (GO) agglomerates on the workability, hydration, microstructure, and compressive strength of cement paste were addressed. The workability of cement paste was reduced because of the presence of GO agglomerates, which entrap a large amount of water. The mini-slump diameter was reduced by 21% with the incorporation of 0.03% by weight GO in cement paste. Hydration of the cement paste was accelerated due to nucleation sites provided by GO agglomerates serving as seeding material in the cement paste. The incorporation of GO refined the pore structure of the cement paste. The incorporation of GO was found to have much greater impact on macropores than on large and small mesopores. At 28days, the incorporation of 0.04% by weight GO produced a 14% improvement in the compressive strength of cement paste. Below 0.03%, the incorporation of GO had no positive effects on compressive strength.

Design and Preparation of Carbon Based Composite Phase Change Material for Energy Piles.

Energy piles—A fairly new renewable energy concept—Use a ground heat exchanger (GHE) in the foundation piles to supply heating and cooling loads to the supported building. Applying phase change materials (PCMs) to piles can help in maintaining a stable temperature within the piles and can then influence the axial load acting on the piles. In this study, two kinds of carbon-based composite PCMs (expanded graphite-based PCM and graphite nanoplatelet-based PCM) were prepared by vacuum impregnation for potential application in energy piles. Thereafter, a systematic study was performed and different characterization tests were carried out on two composite PCMs. The composite PCMs retained up to 93.1% of paraffin and were chemically compatible, thermally stable and reliable. The latent heat of the composite PCM was up to 152.8 J/g while the compressive strength of cement paste containing 10 wt % GNP-PCM was found to be 37 MPa. Hence, the developed composite PCM has potential for thermal energy storage applications.

The influence of variable gypsum and water content on the strength and hydration of a belite-calcium sulphoaluminate cement

ABSTRACTThe relative impact and interaction of two components, gypsum and water, in high ye’elimite containing calcium sulphoaluminate-belite cement pastes at an age of 7 days was studied to find the optimum conditions for compressive strength. Using statistical analysis of 149 compressive strength results having a range of water and gypsum contents, the statistical significance of the variables was investigated. X-ray diffraction analysis demonstrated the different hydration processes occurring within samples based on water and gypsum contents, while mercury intrusion porosimetry comparison confirmed the importance of pore structure towards determining ultimate paste strength. Thermodynamic modelling was also used to contribute to the understanding of the microstructural development. The compressive strengths of cement pastes with varying gypsum and water content were shown to be influenced by both factors, with a non-linear dependence on gypsum content observed.

The Role of Sintered Clay Brick Powder During the Hydration Process of Cement Pastes

The effect of sintered clay brick powder (SCBP) on hydration properties of cement pastes was studied by using thermogravimetric and differential thermal analysis (TG–DTA), scanning electron microscopy and X-ray diffraction techniques in this paper, and the compressive strength was also tested. The test results indicate that the compressive strength of cement pastes decreases with the increase in SCBP content, but improves with the increase in the fineness of SCBP and curing temperature. Although SCBP in cement paste has little effect on the type of hydration products, it significantly affects the amount of the hydrates, especially for Ca(OH)2. The amount of Ca(OH)2 in cement pastes reduces with the increase in SCBP content and curing age, while its microstructure is relatively dense, with abundance of calcium silicate hydrate gel (C–S–H) existing. SCBP in cement paste has high pozzolanic activity, especially for the finer SCBP and after higher temperature curing.