Neat Cement Paste Research Articles

Transient nonlinear vibration characterization of building materials in sequential impact scale experiments

Characterizing standard building materials such as concrete is challenging primarily because of the broad range of constituent component sizes within the material itself. Concrete, the most ubiquitous building material, contains critical components that span at least three orders of magnitude of physical size. This work introduces a nondestructive sequential impact test to extract transient nonlinear vibration behaviors that provide statistically significant holistic characterization of a heterogeneous building material, neat cement paste, on a centimeter scale sample. The sensitivity of the single impact vibration combined with the repeatability of the new sequential apparatus enables the extraction of statistically distinct transient nonlinear (slow dynamic) material memory behaviors. Experimental results on neat cement paste prisms and borosilicate glass blocks across several environmental states and damage conditions reveal an underlying phenomenon of transient nonlinear behaviors. Material damage and moisture state significantly affect the proper interpretation of the transient nonlinear material behaviors. The presented testing procedure and observations, supported by historical experiments, confirm that sequential impact reports a consistent transient nonlinear vibration behavior, and the measured behavior can identify damaged heterogeneous building materials.

Thixotropic and hydration effects of Mg/Al-layered double hydroxide and sodium montmorillonite composite dispersion on oil well cement paste

Thixotropic cement paste, which destroys the grid structure under shear action and rapidly recovers its previous state after a standstill, is an effective method to solve cementing leakage and gas migration issue for oil and gas well cementing. To overcome the shortcomings of clay thixotropic agents (e.g., poor fluidity and mechanical properties with high dosage), we developed a composite nanoclay thixotropic agent (i.e., LDH/MMT) that consists of Montmorillonite (MMT) with permanent negative charges in laminates and Magnesium/Aluminum sulfate-type hydrotalcite (Mg/Al–SO42−-LDHs) with positive charges in laminates. The rheological performance of LDH/MMT and its effects on cement paste were investigated. Results showed that Mg2Al-LDH with a high charge density of laminates significantly improved the gel strength of LDH/MMT dispersion at rest, whereas the apparent viscosity at a high shear rate was slightly affected. When mixed with cement, LDH/MMT at a low dosage endows the cement paste with high yield stress and outstanding shear thinning and thixotropic behavior by forming dynamic reversible “house of card” grid structure between cement and clay colloidal particles. Moreover, compared with neat cement paste, the increment in the compressive strength of cement pastes containing 0.3 %bwoc LDH/MMT was approximately 10% because of the pozzolanic effect and nucleation sites for the growth of hydrated calcium silicate.

Study on mechanical properties of the interfacial transition zone in carbon nanofiber-reinforced cement mortar based on the PeakForce tapping mode of atomic force microscope

In this study, the PeakForce quantitative Nanoscale Mechanical Characterization (PF-QNM) mode was used to explore the micro-zone mechanical properties of the interfacial transition zone (ITZ) in carbon nanofiber (CNF)-reinforced cement mortar. It was found that adding CNFs increased the Young’s modulus of neat cement paste and cement mortar specimens by 15.5% and 36.7%, respectively. The morphology of the interface in a mortar specimen under the PF-QNM mode showed the close embedding of fine aggregates in set cement, which may facilitate force transmission and energy dissipation. The filling and bridging effects of CNFs may increase the Young’s modulus of set cement. The flexural strengths and Young’s modulus of specimens were measured by macro-mechanical tests; the results of which were found to be consistent with the results of micro-zone mechanical property tests. The convenience and accuracy of the test results of the PF-QNM mode were found to be promising.

Multi-scale structure of in-situ polymerized cementitious composites with improved flowability, strength, deformability and anti-permeability

In-situ polymerization of polymers with cement can greatly improve the engineering performances of cementitious composites, the structural mechanisms, however, remain still not fully established. Herein in-situ polymerization modified cementitious composites (iPMCC) with sodium acrylate (SA) in different dosages (0%, 4% and 8%) were fabricated. Flowability, strength, deformability, and water sorptivity of the iPMCCs were tested, and the multi-scale structures in terms of pore size distribution, microscopic morphology, chemical characteristics, and solid structure of calcium-silicate (-aluminate)-hydrates were characterized. Results demonstrate that, compared with neat cement paste, the iPMCC with 4% SA showed the improvement of flowability by 35.1%, the increases of flexural and compressive strength by 109.0% and 11.8%, the rises of flexural and compressive deformation energy by 458.8% and 161.0%, and the decrease of water sorptivity by 19.1%. The in-situ SA polymerizations lead to substantial pore refinement, but macro defects in the iPMCC with 8% SA. Cross-linked sodium polyacrylate networks formed in the cement matrix and interacted with the cement hydrates, accounting for the improved strength, deformability, and water resistance. Cement hydration depression by polymers was evidently supported by the NMR data. The findings would deepen the understandings of multi-scale structure of cementitious composites with polymers, enabling development of highly ductile and durable construction materials.

Anomalous matrix and interlayer pore structure of 3D-printed fiber-reinforced cementitious composites

Ordinary 3D-printed neat cement paste generally possesses a porous interface between two neighbored filaments. Our work demonstrates that the addition of glass microfibers into cementitious slurries may lead to an anomalous pore structure, i.e., the increased porosity of the inner and outer matrices in filaments and the densified interlayer between filaments in fiber-reinforced cementitious composites (FRCC). Limited glass microfiber addition (0.6%) has no benefits to the bending strength of FRCC beams, the compressive strength of filament matrix, and the bonding behaviors between filaments. The coupled mechanisms of lubrication layer and pressurized bleeding on the surface of filaments, and air-void entrapments in the matrix of filaments were proposed to account for the formation of the anomalous pore structure and strengths. Our findings would deepen the understanding of matrix-interlayer structures in 3D-printed FRCC towards better tuning and design of 3D printing-based additive manufacturing.

Investigation on fundamental properties and chemical characterization of water-soluble epoxy resin modified cement grout

In order to improve the defects of conventional cement-based grout such as low strength, brittle failure, weak bonding, and poor stability, water-soluble epoxy resin was designed and used to modify cement-based grout. The purpose of this study is to investigate the feasibility of water-soluble epoxy resin as a high-performance tunnel grouting modifier through the rheological and mechanical properties analysis and chemical characterization of composite grout with different epoxy content and water-cement ratio. The results demonstrated that the fluidity of epoxy resin modified composite grout increased first and then decreased with the addition of epoxy resin. The addition of epoxy resin effectively reduced the bleeding ratio, and kept the grouting fluidity for a certain period of time after mixing. The average particle size of composite grout decreased. Epoxy resin particles and cement particles had opposite zeta potential, and electrostatic attraction occurred in the suspension. The absolute value of zeta potential first increased and then decreased with the increase of epoxy resin. The uniaxial compressive strength and splitting tensile strength of composite grout were observably improved by the modification of epoxy resin, and the ultimate strain was also significantly increased under high epoxy content, and the brittle failure characteristics of the material were improved. With the increase of the content of epoxy resin, the yield of calcium hydroxide in the hydration products increased while the content of calcium carbonate decreased. Epoxy resin contributed to the hydration reaction of cement, while excessive epoxy resin formed a film structure inside to restrict further hydration. The modification of epoxy resin significantly improved the bonding ability of composite grout, and the epoxy resin was uniformly distributed inside the composite grout. The core of the chemical reaction in the modification process was the reaction between free calcium ions and –OH in epoxy resin, and a complex cross-linking network structure was formed with calcium ions as the node. Compared with neat cement paste, epoxy resin modified composite grout had obvious advantages in strength, ultimate strain, fluidity, stability, and bonding ability, so it had broad research potential and application prospect.

Effect of Addition of Alccofine on the Compressive Strength of Cement Mortar Cubes

In the modern era, many research works are going on throughout the world for finding suitable cementitious material for the replacement of cement since it causes environmental pollution. In this order Fly ash, Silica fume, GGBS, Metakaolin, Micro materials, Quartz powder, etc. are tried out for replacing partially or fully the cement in concrete. A new ultrafine material called Alccofine (AF) which is manufactured from glass wastes is tried out for replacing partially in this research. Compressive strength is one of the important properties of cement. Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Cement mortar of 1:3 mix proportion is used to cast the cubes having an area of 50 cm2 are used for the determination of compressive strength of cement as per IS: 4031-1988 (Part-6). The graded Indian Standard sand (Ennore Sand -ES) confirming to IS: 650-1991 is used for preparing the cubes. In the same mix proportion, the same size cubes are cast with the River Sand (RS) to study the difference of the compressive strength between the Indian standard sand and river sand. Ordinary Portland cement (OPC) and Portland Pozzolana Cements (PPC) are used. The present study is the influence of Alccofine on cement mortar cubes by replacing the cement by Alccofine with various proportions like 5%, 10%, 15%, 20% were cast and tested in the laboratory as per Indian Standard 4301-1988 (Part-6) and the results were analysed and presented in the form of charts and graphs. It is observed that the early age strength is obtained for all the combinations but 10 percent of Alccofine yields more strength than other dosages. Doi: 10.28991/esj-2021-01265 Full Text: PDF

Decrease in Viscosity Caused by Agglomeration and Particle Dispersion in Cement–Fly Ash Suspensions

Incorporating fly ash in a concrete mix significantly improves its consistency, resulting in lower viscosity. It is believed that the spherical shape of the fly ash particles is the main cause of the low viscosity. However, the physicochemical causality of the fly ash effect has not been deeply studied and there have been only limited experiments on the particles’ interactions. The use of laser backscattering measurement in this paper allowed the investigation of the agglomeration and dispersion of fly ash particles in an in situ paste. It was found that agglomerates composed of mixed particles develop in a fly ash–cement paste. Their dimensions are comparable to those in neat cement paste. More importantly, incorporating nano-scale spherical dispersed fly ash particles in the mix provides a ball-bearing effect between the micro-scale agglomerates. The viscosity of the mix consequently decreases.

The Behavior of Superabsorbent Polymers (SAPs) in Cement Mixtures with Glass Powders as Supplementary Cementitious Materials.

The absorption and desorption of superabsorbent polymers (SAPs) in cement mixtures containing two different glass powders as supplementary cementitious materials are examined in this paper. Two SAPs with different chemical compositions were synthesized in-house and used in the experiments. SAP absorption was investigated directly through the mass change of SAPs in cement slurries, as well as indirectly using the flow test. Scanning electron microscopy was used to monitor the desorption of SAPs using samples prepared with freeze-drying. Hydration and setting time were evaluated to explain the desorption behavior of SAPs. SAP absorption generally increased in pastes with glass powders. The desorption rate of SAPs in different pastes was shown to correlate with the onset of solid skeleton development in the pastes. The addition of SAPs reduced autogenous shrinkage in neat cement paste more than in pastes with glass powders.

Effect of endogenous chloride contamination on the electrochemical and hydration responses of reinforced Belite-Ye'elimite-Ferrite (BYF) cement mortars

Carbon steel rebars passivate in Belite-Ye'elimite-Ferrite mortars, despite the initial low pH of the pore solution compared to Portland equivalents. Besides passivation ability, another important durability issue is the maximum allowed chloride content in the fresh mix beyond which passivation is prevented, normally 0.4% of chloride by cement mass for reinforced Portland concretes. This work aims to evaluate the impact of different endogenous chloride contents on the evolution of the electrochemical and physicochemical responses of reinforced mortars and neat cement pastes. It is shown that steel in BYF mortars contaminated with up to 0.4% of chlorides effectively passivate but the time needed to passivation is longer than for OPC mortars. Sodium chloride contamination was also found to retard the BYF hydration due to a delayed belite and ferrite hydration. Results showed that higher w/c ratio decreases the tolerable chloride content from 0.4%, BYF (w/c = 0.50) to 0.2%, BYF (w/c = 0.67).

Performance of irradiated blended cement paste composites containing ceramic waste powder towards sulfates, chlorides, and seawater attack

Within the scope of this study, blended cement pastes were prepared by replacing different proportions of ordinary Portland cement with ceramic waste powder (CWP). The hardened blended cement pastes were cured under tap water for different periods of time up to 180 days. Physico‐mechanical properties of specimens were studied in terms of free lime content, chemically combined water, compressive strength, and particle size distribution. The results manifested that the optimum content of ceramic waste which gave a marked improvement in the mechanical properties was 10% as compared to the other specimens at the same curing age. Besides that, similar specimens of the hardened blended cement paste containing 10% CWP were impregnated with unsaturated polyester and exposed to different doses of gamma rays from 10 to 50 kGy. Both the impregnated specimens that irradiated at a dose of 30 kGy and the neat blended cement paste that contained 10% ceramic waste were soaked in 1, 3, and 5% magnesium sulfate, sodium chloride solutions, and in seawater for up to 180 days. The results indicated that the composite specimens became more resistant to aggressive solutions and their durability increased as compared to the neat blended cement paste prepared under the same previous conditions. J. VINYL ADDIT. TECHNOL., 26:24–34, 2020. © 2019 Society of Plastics Engineers

Performance Testing of Hydraulic Cements: Measuring Sulfate Resistance

The sulfate resistance of cements used in the construction industry is traditionally assessed by measuring the expansion of a prism of 280 mm (11inch) length and 25 mm (1 inch) square cross section immersed in a sodium sulfate solution for at least one year. The duration of the experiment limits this test from being used as a performance-based determination of innovative mixtures of cementitious materials. In response to the need for a more rapid test protocol, the National Institute of Standards and Technology (NIST) has developed a new test method that measures the expansion of smaller bars (10 mm × 10 mm × 60 mm) made with neat cement paste. With these bars, similar expansion is achieved in less than 3 months, reducing the test duration by a factor of at least 4. This accelerated test method provides more rapid results consistent with the traditional test procedure, allowing for a shorter decision time and the screening of more materials.

Influence of PCE kind and dosage on ettringite crystallization performed under terrestrial and microgravity conditions

AbstractEarly ettringite crystallization in the presence of 2 chemically different polycarboxylate superplasticizers was studied by hydrating a commercial portland cement (CEM I 52.5 N) for 10 seconds. It was found that the presence of polycarboxylate superplasticizers leads to ettringite crystals which are longer, yet slimmer (higher aspect ratio), compared with the crystals obtained from neat cement paste. This finding suggests that the polycarboxylate (PCE) polymers predominantly adsorb on the lateral faces of the hexagonal‐prismatic crystals of ettringite. For the methacrylate‐based PCE, this effect increases with increasing superplasticizer dosage, whereas for the IPEG‐PCE, the effect achieved at a very low dosage (0.05%) is not altered when dosage increases. The behaviors of both PCE polymers can be explained by their different adsorption behavior, whereby the IPEG‐PCE reached the saturated adsorbed amount at much lower dosage than the MPEG‐PCE. Microgravity only has a minor effect on the growth of ettringite. There, generally smaller crystals are observed.

SEM-backscattered electron imaging and image processing for evaluation of unhydrated cement volume fraction in slag blended Portland cement pastes

Proper parameters for image taking and minimum field number for image processing were investigated to evaluate volume fraction of unhydrated cement(UHC) in both neat cement paste and slag blended cement paste. Our research suggested that magnification 250× was sufficient for the two pastes, and accelerating voltage should be set as 15 kV and 20 kV for BSE image taking of neat cement paste and slag blended cement paste respectively; the minimum field number increased while the total imaging area stayed the same as the magnification increased within certain statistical bias.

Estimating the original cement content and water–cement ratio of Portland cement concrete and mortar using backscattered electron microscopy

In a previous study, a method was proposed to estimate the cement content, water content, free water–cement ratio (w/c) and degree of hydration of hardened Portland cement pastes that have unknown proportions. The method is based on measuring the volumetric fractions of capillary pores, hydration products and unreacted cement using backscattered electron microscopy and the volumetric increase of solids during cement hydration. It has the advantage that it is quantitative and does not require comparison with reference samples made with the same materials and cured to the same hydration degree as the unknown sample. However, the method was tested on neat cement pastes only, hence limiting its practical application. In this paper, the extension of the method to Portland cement mortars and concretes is presented, and results are provided, obtained from samples made with three cement types and a range of aggregate content (40–70% vol.), w/c ratio (0·30–0·70) and curing age (3–90 days). The study also involved sealed-cured, wet-cured and field-exposed samples. It is observed that bleeding and aggregate absorption can have a significant effect on the free w/c ratio. Overall, good agreement between the estimated and actual values is found. The error in estimating free w/c ratio using the proposed method is no more than 0·05 for all samples tested in this study.

Quantitative Characterization of Hydration of Cement Pastes by Rietveld Phase Analysis and Thermoanalysis

The quantitative characterization of hydration of cement pastes has always been one of focuses of researchers’ attention. Rietveld phase analysis (RPA), a combination of quantitative X-ray diffraction (QXRD) and the Rietveld method, supplies a tool of an enormous potential for that. Although a few of related researches were conducted by RPA, the reported attention was not paid to the neat cement paste with a low w/c ratio. Therefore, this work aimed at the quantitative study on hydration of such a cement paste chiefly by this method, meanwhile, cooperated with the hyphenated technique of thermogravimetry with differential scanning calorimetry (TG-DSC), as a spot check. Results indicated that RPA was a reliable method in quantitatively characterizing hydration of cement pastes, and gave a clear decription of evolution of all main crystal phases in cement pastes; and that the evolution of monosulphate(Afm_12) was also able to be tracked quantitatively. This will help to understand better the hydration mechanism of cement pastes, as well as to investigate quantitatively effects of mineral and chemical admixtures on hydration of composite cementitious systems.

Effect of addition of nano-magnetite on the hydration characteristics of hardened Portland cement and high slag cement pastes

In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe3O4 nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe3O4 nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character.

Evolution of Various States of Water in Blended Cementitious Materials

Low field NMR, as a nondestructure and noninvasive method was employed to study the evolution of various states of water in blended cementious materials added with fly ash during hydration from 1 day to 100 days. The relative content of water held in series of pores in cement matrix, e.g. capillary pore, mesopore and gel pore, was determined based on the quantitative relationship between transverse relaxation time, T2, and pore dimension. The results indicated that the relative content of chemically bound water was higher at long-term cure of 100 days compared with the neat cement paste. The water distributed in various pores was also influenced by the pozzolanic reactions between fly ash and calcium hydroxide. The gel water and mesopore water increased dramatically during the short-term age of 1 to 7 days in blended matrix, but then decreased gradually after 28 days, unlike that in pure cement paste. Due to the lower hydration degree in blended matrix, there was still amount of capillary water residual in paste to supply for the further hydration of fly ash.

Ultrafiltration Treatment and Physical Properties of Ammonia Sulfite Pulping Liquor of Wheat Straw

Ammonia sulfite pulping liquor of wheat straw was treated by ultrafiltration. Experimental results indicated that the membrane with a cut-off of 10kDa was suitable for concentrating wheat straw liquor and had good anti-fouling property against pulping liquor. Permeability of ash turn higher with the increasing of volume reduction at the operating condition of 200 kPa and 25°C, and retentate was concentrated when volume reduced. Influences of ultrafiltration on physical properties of ammonia sulfite pulping liquor and its retentate after ultrafiltration were studied. Results showed that retentate had better performances as surfactant, concrete additive and dispersant. Surface tension of 1% lignin solution of retentate was 54.7 mN/m, which was lower than that of the untreated original lignosulfonate by 2.2 mN/m. Dispersing effect of retentate on cement was also investigated, it was found that flowability of neat cement paste improved from 70mm to 102mm.

Effect of Naphthalene Compounded Superplasticizer on Strength and Shrinkage of Ready-Mixed Concrete

Superplasticizer is widespread applied in the ready-mixed concrete in China. In the specific engineering, it is not only has the requirement of water-reducing ratio for superplasticizer, but also the superplasticizer has to meet the demand such as early-strength, air-entraining, retarding and so on. In current, the naphthalene compounded superplasticizer is conducted on the basis of the FDN modification. This paper selects two kinds of representative naphthalene compounded superplasticizers, one is the setretarder superplasticizer (WRA1), and the other one is the early strength-air entraining-retarding superplasticizer (WRA2). The effect of performance on neat cement paste, mortar and concrete which mixed with the two admixtures are compared with the benchmarks (not mixed with water reducing agent) and mixed with FDN. Through the analysis and comparison of the test data, the general rules of the naphthalene compounded superplasticizer to concrete strength and shrinkage are put forward in this paper. Also, according to those rules, it poses the concrete problems to be noted in the production. This may have guidance for reducing the early cracks of ready-mixed concrete.