Compressive Strength Of Cement Paste Research Articles

Study on modification mechanism of workability and mechanical properties for graphene oxide-reinforced cement composite

Graphene oxide/cement composite was prepared using a graphene oxide aqueous solution. The workability and mechanical properties of graphene oxide/cement composite with different concentrations for graphene oxide and the ratio of water to cement were investigated. The results observed were the fluidity of cement pastes decreased noticeably with the addition of graphene oxide and increased with the increase in the ratio of water to cement for all tested samples of different graphene oxide contents. It is indicated that a noticeable inverse correlation between the concentration of graphene oxide and fluidity was observed, and a positive linear relationship between the ratio of water to cement and fluidity was also obtained. The compressive strength of cement pastes significantly improved in the presence of an appropriate concentration of graphene oxide as compared to that of the cement paste without graphene oxide; this difference was due to the denser microstructure of graphene oxide/cement composite than that of the control specimens. With the combined analysis of X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry, the results showed that graphene oxide could promote and regulate the formation and connection of calcium hydroxide and calcium silicate hydrate during the hydration reaction, forming numerous regular and extremely compact plate-shaped crystals, and the compact plate-shaped microstructures constituted of not only calcium hydroxide and calcium silicate hydrate but also wrapped ettringite. This investigation will provide a flexible way to preparation of graphene oxide/cement composite with wanted fluidity and optimized compressive strength that promote the industry application of graphene oxide/cement composite.

Effects of Sand Powder on Sulfuric Acid Resistance, Compressive Strength, Cost Benefits, and CO2 Reduction of High CaO Fly Ash Concrete

This article studies the efficiency of sand powder as a supplementary cementitious material (SCM) in improving the sulfuric acid resistance of concrete incorporated with high CaO fly ash. Besides, the effects of sand powder on compressive strength development, mitigation of carbon dioxide emission, and cost‐effectiveness are addressed. Paste mixtures with W/B ratios of 0.25 and 0.40 were used in this study for the performances of sulfuric acid resistance and long‐term compressive strength development. The test results indicated that sand powder could reduce the weight loss of the tested paste specimens in sulfuric acid solution with a pH of 1, compared to the control specimens, especially for the specimens incorporated with high CaO fly ash. The sand powder addition could also increase the compressive strength of cement pastes at the age of 90 days by 26.27% and 43.80% for W/B ratios of 0.25 and 0.40, respectively. The use of sand powder in the evaluated concrete mixture could also reduce CO2 emission by 23.23% and lower the cost of the mixtures by 8.05%, compared to the control mixture. The addition of sand powder could significantly increase the sulfuric acid resistance, compressive strength, and economic benefits and reduce the CO2 emission of high CaO fly ash‐cement‐based materials.

COMPLEX MODIFYING ADDITIVES FOR CEMENT CONSTRUCTION MIXES

It is currently relevant to study the use of local waste based on mineral finely dispersed additives similar to substances that are formed as a result of cement hydration, which ensures high quality, increases frost resistance and forms a dense dissolved mixture. Reducing the consumption of a binder in mortar and concrete mixtures due to the introduction of modifying additives is also an important research field. The paper presents the results associated with pro-ducing a complex modifying additive consisting of waste products from marble and silicon di-oxide nanoparticles and its effect on the properties of cement systems. It is shown that the introduction of a modifying additive, while reducing cement consumption, can increase the compressive strength of cement paste up to 56 %. The X-ray phase analysis is used to determine the composition of the modified cement paste. The efficiency of using marble production wastes together with SiO2 nanoparticles as a complex modifying additive is evaluated to im-prove the properties of the cement mix.

Combined effects of biochar and MgO expansive additive on the autogenous shrinkage, internal relative humidity and compressive strength of cement pastes

Internal curing and expansive additives are normally used to mitigate the autogenous shrinkage of cement materials. Biochar, with a porous microstructure and water holding capacity, has a potential to be used as a novel internal curing agent, whereas few work was focused on its impact on the autogenous shrinkage of cement materials. The present work aims to investigate the effects of biochar and its combination with MgO expansive additive (MEA) on the internal relative humidity, autogenous shrinkage, compressive strength as well as microstructures of the cement pastes via using humidity sensor, laser displacement measurer, MIP, TG/DSC, and SEM. Results indicated that, compared to the plain cement paste, incorporation of biochar provided efficient internal curing, maintaining a higher internal relative humidity and hence a reduced the autogenous shrinkage by 16.3% at the age of 180 h. An obvious synergetic effect on mitigating the autogenous shrinkage of cement paste was observed when the biochar was added with the combination of MEA in the cement paste. For instance, with the addition of 2 wt% biochar and 8 wt% MEA with a high reactivity (reactivity value of 45 s) gained an expansion of 80 microstrain rather than a shrinkage at the age of 180 h. Addition of biochar increased slightly the compressive strengths of the cement pastes at the late ages of 28d and 90d. This facilitates to offset partially the compromise on compressive strength of cement paste caused by the incorporation of MEAs alone. This study provides a novel and effective approach for mitigating the autogenous shrinkage of cement materials.

Effect of water resistant SiO2 coated SrAl2O4: Eu2+ Dy3+ persistent luminescence phosphor on the properties of Portland cement pastes

The present study investigates the effect of water-resistant SiO2 coated SrAl2O4: Eu2+, Dy3+ (SSA) phosphor on the properties of Portland cement pastes. In order to investigate it, firstly, SrAl2O4: Eu2+, Dy3+ phosphor was coated with SiO2 using heterogeneous precipitation method. Afterward, coated phosphor was admixed with Portland cement in varying proportions to prepare cement pastes. The setting time, hydration reaction, compressive strength, and luminescence intensity analysis were carried out. Moreover, water resistance performance of SSA phosphor based cement pastes was assessed in terms of afterglow test. Based on the results of setting time and hydration studies, it was deduced that SSA phosphor has set acceleration effect on cement pastes. Use of SSA phosphor improved the compressive strength of cement pastes due to the greater degree of hydration. Moreover, the afterglow study results confirmed the hydrolysis stability of SSA phosphor in water cured cement pastes. The XRD, SEM, EDX, TG-DTG, and FTIR analyses confirmed the formation of excessive amount of hydration products in SSA phosphor based cement pastes. Based on the results obtained, it is concluded that using SSA phosphor could be a promising approach for producing water-resistant persistent luminescence light emitting cement composites.

Microstructure of calcium carbonate whisker reinforced cement paste after elevated temperature exposure

Calcium carbonate whisker (CW) could improve mechanical properties of cementitious composites at room temperature. Aiming at using CW as high-performance and low-cost microfiber at high temperature, the microstructural changes of cementitious composites with CW exposed to high temperature are clarified in this research. From room temperature to 500 °C, additional hydration of unhydrated binder grains in steam environment occur (“internal autoclaving”). Moreover, CW transferred from aragonite to calcite in cement paste at about 375 °C (“phase transformation”). Under these coupling effects, calcite CW forms stronger bond with these rehydration products than that at room temperature, also improving the pore distribution and compressive strength. At 800 to 1000 °C, CW increases the pore size and decreases the compressive strength of cement paste due to CW decomposition. From 1000 to 1100 °C, the residual compressive strengths of CW reinforced cement pastes increase slightly because of the forming of calcium silicate and Ca(OH)2.

Modeling early age hydration reaction and predicting compressive strength of cement paste mixed with expansive additives

Although expansive additives have been widely used to efficiently reduce shrinkage cracking in concrete, little research has been undertaken to model the hydration reaction of cement and expansive additive blends. This paper presents a hydration model that describes the hydration reaction that occurs when expansive additives are mixed at an early stage and an equation to predict the compressive strength of expansive concrete. Using the proposed model, this study predicted the hydration degree, rate of heat evolution, and gel/space ratio of the hardening cement–expansive additive paste. The results indicated good agreement of the calculated data with the measured data. From the relationship between the gel/space ratio and compressive strength, an equation was deduced for prediction of the development of compressive strength of expansive concrete. Furthermore, this work also found that the model parameters can be represented as a function of the mineral composition of the cement. The results demonstrate that the proposed model is effective and useful in predicting the hydration and mechanical properties of expansive concrete.

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