Effects of Fe2O3 Nanoparticles on Water Permeability and Strength Assessments of High Strength Self-Compacting Concrete

In this work,compressive,flexural and split tensile strength together with coefficient of water absorption of high performance self-compacting concrete containing different amount of Fe2O3 nanoparticles have been investigated.The strength and the water permeability of the specimens have been improved by adding Fe2O3 nanoparticles in the cement paste up to 4.0 wt%.Fe2O3 nanoparticle as a foreign nucleation site could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount especially at the early age of hydration and hence increase the strength of the specimens.In addition,Fe2O3 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability.Several empirical relations have been presented to predict the flexural and the split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.Accelerated peak appearance in conduction calorimetry tests,more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results indicate that Fe2O3 nanoparticles up to 4 wt% could improve the mechanical and the physical properties of the specimens.     

Concrete with ceramic waste aggregate

Use of hazardous industrial wastes in concrete-making will lead to greener environment. In ceramic industry about 30% production goes as waste, which is not recycled at present. In this study an attempt has been made to find the suitability of the ceramic industrial wastes as a possible substitute for conventional crushed stone coarse aggregate. Experiments were carried out to determine the compressive, splitting tensile and flexural strengths and the modulus of elasticity of concrete with ceramic waste coarse aggregate and to compare them with those of conventional concrete made with crushed stone coarse aggregate. The properties of the aggregates were also compared. Test results indicate that the workability of ceramic waste coarse aggregate concrete is good and the strength characteristics are comparable to those of the conventional concrete.     

Limestone dust and glass powder wastes as new brick material

Large amounts of glass and limestone wastes are accumulating all over the world. Disposal of Limestone Powder Waste (LPW) and Waste Glass Powder (WGP) is a rapidly growing problem for some municipalities, so research for alternative utilization of these disposals is needed. In this respect, the objectives of this study are to investigate both physical and mechanical properties of samples containing LPW–WGP combinations for producing as new building brick material. An experimental approach to develop a new brick material including mainly LPW, a small quantity of Portland cement and WGP is presented. The LPW, WGP and cement are mixed, humidified and compacted under high pressure in the moulds. The values of compressive strength, flexural strength, unit weight, water absorption, abrasion resistance, freezing–thawing (F-T) resistance and thermal conductivity satisfy the relevant international standards and introduces smoother surface compared to the current concrete bricks in the market. The process undertaken can easily be applied within the current brick plants. The WGP used in LPW remarkably improves the compressive strength, flexural strength, modulus of elasticity, abrasion resistance, F-T resistance, and thermal conductivity of LPW brick samples produced in this study. The test results indicate that the samples containing LPW–WGP combinations provide better results for a potential of producing economical new brick materials.     

Influence of various amounts of limestone powder on performance of Portland limestone cement concretes

The benefits of limestone as a partial replacement for Portland Cement (PC) are well established. Economic and environmental advantages by reducing CO₂ emissions are well known. The paper describes the effect of various amounts of limestone on compressive strength, water penetration, sorptivity, electrical resistivity and rapid chloride permeability on concretes produced by using a combination of PC and limestone at 28, 90 and 180 days. The percentages of limestone that replace PC in this research are 0%, 5%, 10%, 15% and 20% by mass. The water/(clinker + limestone) or (w/b) ratios are 0.37, 0.45 and 0.55 having a constant total binder content of 350 kg/m³. Generally, results show that the Portland limestone cement (PLC) concretes having up to 10% limestone provide competitive properties with PC concretes.     

The effect of adding nano-SiO2 and nano-Al2O3 on properties of high calcium fly ash geopolymer cured at ambient temperature

This article presents the effect of adding nano-SiO₂ and nano-Al₂O₃ on the properties of high calcium fly ash geopolymer pastes. Nano-particles were added to fly ash at the dosages of 0%, 1%, 2%, and 3% by weight. The sodium hydroxide concentration of 10 molars, sodium silicate to sodium hydroxide weight ratio of 2.0, the alkaline liquid/binder ratio of 0.60 and curing at ambient temperature of 23 °C were used in all mixtures. The results showed that the use of nano-SiO₂ as additive to fly ash results in the decrease of the setting time, while the addition of nano-Al₂O₃ results in only a slight reduction in setting time. Adding 1–2% nano-particles could improve compressive strength, flexural strength, and elastic modulus of pastes due to the formation of additional calcium silicate hydrate (CSH) or calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) or geopolymer gel in geopolymer matrix. In addition, the additions of both nano-SiO₂ and nano-Al₂O₃ enhances the shear bond strength between concrete substrate and geopolymer.     

石灰石粉对泵送混凝土性能影响的试验研究

本文主要研究了单掺石灰石粉、石灰石粉与粉煤灰复掺对泵送混凝土拌合物工作性和抗压强度的影响,研究表明：掺加石灰石粉可以改善泵送混凝土的工作性能,与单掺石灰石粉相比,石灰石粉与粉煤灰复掺,具有复合叠加效应,不仅可以改善泵送混凝土的工作性能,同时可提高泵送混凝土的抗压强度。     

Properties of cold bonded quarry dust coarse aggregates and its use in concrete

In this study, artificial coarse aggregates are prepared by a cold bonding technique. The waste materials, namely, fly ash and quarry dust, are used for the preparation of the cold bonded artificial aggregate. Portland cement is used as the binder material. The independent variables considered for the preparation of the artificial aggregate are cement and fly ash contents. The properties of the artificial aggregate are determined and regression models are proposed for predicting these properties. The strength and workability of concrete containing artificial aggregate is determined. The slump loss of concrete containing artificial aggregate is found to be gradual. The concretes with strengths of up to 30 MPa is prepared using artificial aggregates. The study promotes the use of waste material and supports sustainable construction practices.     

石粉对水泥-矿粉混凝土性能的影响

本文主要研究了石粉对水泥-矿粉混凝土的工作性、抗压强度、耐久性能(抗渗性能、抗碳化性能和抗冻性能)的影响,并利用孔结构微观分析对其进行了机理分析。研究表明:石粉应用于水泥-矿粉混凝土中,不仅可改善混凝土的工作性能,而且可提高混凝土的抗压强度,对混凝土的耐久性能(抗渗性能、抗碳化性能和抗冻性能)影响不大。     

A linguistic model for evaluating cement strength

This paper presents a soft methodology for predicting the 28-day compressive strength of Portland cement (CCS) by making use of the 1-day, 3-day and 7-day CCS values. Data taken from a cement plant in Turkey have been employed in the model construction and testing. For implementation, linguistic models were designed based on if-then fuzzy rules. In addition, predictions of these models were compared with results of the regression models. The performance evaluations showed that the linguistic-based fuzzy predictions are very satisfactory in estimating cement strength and the linguistic modeling performs better than regression modeling.     

Contribution of limestone to the hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements can be blended with mineral additions such as limestone for properties and cost optimization. This study investigates the contribution of limestone to the hydration of a commercial CSA clinker regarding the hydration kinetics, hydrate assemblage and compressive strength. Nine formulations were defined at M-values of 0, 1.1 and 2.1 (M = molar ratio of anhydrite to ye’elimite) without and with medium and high limestone contents.Calorimetric results indicate that limestone accelerates the hydration reaction especially at M = 1.1, probably due to the filler effect. The phase assemblages were calculated by thermodynamic modeling using Gibbs Energy Minimization Software (GEMS). With increasing limestone content the formation of ettringite and calcium monocarboaluminate is predicted at the expense of calcium monosulfoaluminate. With increasing M-value more ettringite is predicted at the expense of the monocarbonate and less calcite takes part in the hydration reactions.The modeled results compare well with the experimental data after 90 d of hydration, except that calcium hemicarboaluminate was found instead of monocarbonate, which is assumed to be due to kinetics considerations.The lowest compressive strength occurs in ternary formulations, whereas in the absence of calcium sulfate, strength is significantly higher.The results presented here indicate that in CSA cements, limestone accelerates early hydration kinetics, takes part in the hydration reactions at M < 2, and has a positive effect on strength development in systems without anhydrite.     

Influence of limestone and anhydrite on the hydration of Portland cements

The addition of CaCO₃ and CaSO₄ to Portland cement clinker influences the hydration and the strength development. An increase of the CaSO₄ content accelerates alite reaction during the first days and results in the formation of more ettringite, thus in a higher early compressive strength. The late compressive strength is decreased in Portland cements containing higher quantities of CaSO₄. The reduced late compressive strength seems to be related to an increase of the S/Si and Ca/Si content in the C–S–H.The presence of calcite leads to the formation of hemicarbonate and monocarbonate thus indirectly to more ettringite. Only a relatively small quantity of calcite reacts to form monocarbonate or hemicarbonate in Portland cement. Although hemicarbonate is thermodynamically less stable than monocarbonate, hemicarbonate formation is kinetically favored. Monocarbonate is present only after 1 week and longer independent of the quantity of calcite available and the content of sulphate in the cement.     

Effect of cement type and limestone particle size on the durability of steam cured self-consolidating concrete

This paper describes a laboratory program to investigate the influence of cement and limestone filler (LF) particle size on the hardened properties and durability performance of steam cured self-consolidating concrete. In addition, the interplay between cement type and LF particle size was investigated. CSA (Canadian Standards Association) Type GU (General Use) and HE (High Early-strength) cements were used with 5% silica fume (SF) [1]. The water-to-cement ratio was 0.34. LF with two nominal particle sizes of 17 μm and 3 μm, which correspond to Blaine fineness of 475 and 1125 m²/kg, respectively, were used. In addition to fresh concrete properties, hardened properties including compressive strength, elastic modulus, ultrasonic pulse velocity and density were measured at 12 h and 16 h, and at 3, 7 and 28 days. Indicators of durability performance including rapid chloride permeability testing (RCPT), sulfate resistance, linear shrinkage, salt scaling resistance and freeze-thaw resistance were evaluated. The results showed that LF improved the 12 and 16-h strength with no influence on later age strength (i.e., 3–28 days). The linear shrinkage and RCPT decreased with the addition of LF. This reduction was linked to the production of calcium mono-carboaluminate. LF did not impact the sulfate resistance, salt scaling resistance or freeze-thaw resistance of concrete.     

Optimization of calcium chloride content on bioactivity and mechanical properties of white Portland cement

This research investigates the optimization of calcium chloride content on the bioactivity and mechanical properties of white Portland cement. Calcium chloride was used as an addition of White Portland cement at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10% by weight. Calcium chloride was dissolved in sterile distilled water and blended with White Portland cement using a water to cement ratio of 0.5. Analysis of the bioactivity and pH of white Portland cement pastes with calcium chloride added at various amounts was carried out in simulated body fluid. Setting time, density, compressive strength and volume of permeable voids were also investigated. The characteristics of cement pastes were examined by X-ray diffractometer and scanning electron microscope linked to an energy-dispersive X-ray analyzer. The result indicated that the addition of calcium chloride could accelerate the hydration of white Portland cement, resulting in a decrease in setting time and an increase in early strength of the pastes. The compressive strength of all cement pastes with added calcium chloride was higher than that of the pure cement paste, and the addition of calcium chloride at 8 wt.% led to achieving the highest strength. Furthermore, white Portland cement pastes both with and without calcium chloride showed well-established bioactivity with respect to the formation of a hydroxyapatite layer on the material within 7 days following immersion in simulated body fluid; white Portland cement paste with added 3%CaCl₂ exhibited the best bioactivity.     

The influence of cellulose nanocrystals on the microstructure of cement paste

This paper reports the influence of raw and sonicated cellulose nanocrystals (CNCs) on the microstructure of cement paste. A novel centrifugation method is designed to measure the concentrations of the adsorbed CNCs (aCNCs) on the cement surface, and the free CNCs (fCNCs) which are mobile in water. It is found that, the majority of the CNCs (>94%) are aCNCs. More importantly, sonication does not significantly reduce the amount of aCNCs (reduction of less than 2%). We surmise that, after sonication, the aCNCs are primarily dispersed over the cement surface, instead of becoming fCNCs via sonication. Isothermal calorimetry and energy-dispersive X-ray spectroscopy (EDX) results support this theory. The water desorption tests show that the total porosities of cement pastes with raw and sonicated CNCs are 14.8% and 14.4%, which showed a reduction from 16% for the plain cement paste. The porosity reduction is a result of an increase in the degree of hydration. The advantage of sonicated CNCs is they are dispersed, avoiding therefore agglomerates that can lead to pores, voids, and air entrapment. The nanoindentation results show that the reduced indentation modulus on the interfacial regions between cement particles and the low density CSH is increased when CNCs are used.     

Phase transformations and mechanical strength of OPC/Slag pastes submitted to high temperatures

Ground granulated blast furnace slag (GGBFS or “slag”) is a by product of the steel industry and is often used in combination with ordinary Portland cement (OPC) as a binder in concrete. When concrete is exposed to high temperatures, physical and chemical transformations lead to significant loss of mechanical strength. Past studies have reported changes in concrete where OPC is 100% of the binder, but there is a lack of published data on slag blended cements. This work provides better understanding of how slag blended cement pastes behave when exposed to high temperatures, when the critical transformations occur, and what the consequences in the structure of these pastes are. Thermogravimetric analysis made it possible to identify when the transformations occurred and the changes in mechanical strength in the cement paste. A unique outcome of this work is the lower damage presented by slag blended cements after exposure to high temperatures     

高岭土对混凝土强度的影响因素研究

通过胶砂试验的方法研究了高岭土矿物掺合料对水泥胶砂的影响。由试验结果得知,28天龄期时,随高岭土量的增加,水泥胶砂抗压强度和抗折强度均下降．然而高岭土的细度和煅烧与否胶砂的强度没有影响。     

沥青树脂和炭纤维的复合性能

流化床催化裂化(Fluid catalytic ciracking,FCC)油浆富芳馏份(Fluid catalytic ciracking rich aromatic,FCCRF)与交联剂对苯二甲醇(1,4-benzenedimethanol,PXG)在催化剂对甲基苯磺酸(Para-toluene sulphonic acid,PTS)的作用下,加热至120℃以上,制得的沥青树脂是一种新型的热固性树脂。沥青树脂在一定条件下与炭纤维或炭纤维纸热压成型。成型料在空气中250℃-10h和300℃-2h热处理后,其热力学性能无明显变化;在强酸、强碱中处理1h~70h,质量几乎无变化;说明沥青树脂与炭纤维或炭纤维纸的复合材料热稳定性和化学稳定性尚好。沥青树脂与炭纤维或炭纤维纸的复合材料在高纯氮保护下,经950℃~1000℃热处理后制得炭/炭复合材料,由SEM观察可见炭/炭复合材料无空洞、劈裂,力学性能尚可,断口炭纤维拉出小于10μm,说明沥青树脂与炭有较强的亲和力,与炭纤维黏合很好。FCC油浆富芳馏份制备的沥青树脂,作为炭/炭复合材料的基质是可行的。     

Effect of sodium silicate- and ethyl silicate-based nano-silica on pore structure of cement composites

This study proposes using sodium silicate-based nano-silica (SS) in cement composites. The effect of the addition of the proposed nano-silica on cement composites was compared to that of conventional ethyl silicate-based nano-silica (ES) and silica fume (SF). This study found that the inclusion of SS in cement composites has mainly two effects on their properties: one is a fast pozzolanic reaction, and the other is a pore-filling effect in a cement matrix. As a result, SS dramatically improves the early-age strength of cement composites by up to 184% and 152%, compared to a control specimen and the specimen with ES inclusion, respectively. Calorimetry, X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) tests were conducted to monitor the effects of these nano-silicas.     

Durability and microstructure analysis of CO2-cured cement-bonded wood particleboard

Dry-processed cement-based wood composites are reconstituted wood products with desirable longevity, fire resistance and life cycle cost. In this study, the effects of accelerated aging on the performance of CO₂-cured cement-bonded wood particleboards were investigated. The accelerated aging conditions considered simulated natural aging phenomena. Repeated wetting–drying and freezing–thawing cycles led to increased stiffness and somewhat reduced toughness. X-ray diffraction and thermogravimetric analyses indicated that aging effects led to increased CaCO₃ and decreased Ca(OH)₂ contents in CO₂-cured cementitious composites. Mercury intrusion porosimetry test results indicated that CO₂ curing reduced the capillary pore volume in both unaged and aged boards.     

Microstructure and mechanical performance of modified mortar using hemp fibres and carbon nanotubes

Mechanical performance of modified mortar using hemp fibres is studied following various processing conditions. Hemp fibres combined with carbon nanotubes (CNT) are introduced in mortar and their effect is studied as function of curing time. The cement phase is replaced by different percentages of dry or wet hemp fibres ranging from 1.1 wt% up to 3.1 wt% whereas carbon nanotubes are dispersed in the aqueous solution. Our experimental results show that compressive and flexural strengths of wet fibres modified mortar are higher than those for dry hemp-mortar material. The achieved optimal percentage of wet hemp fibres is 2.1 wt% allowing a flexural strength higher than that of reference mortar. The addition of an optimal CNT concentration (0.01 wt%) combined with wet hemp has a reinforcing effect which turns to be related to an improvement of compressive and flexural strengths by 10% and 24%, respectively, in comparison with reference condition.