Recycling of polyurethane foam waste in the production of lightweight cement pastes and its irradiated polymer impregnated composites

This study aimed at using polyurethane foam waste in the production of lightweight white cement pastes by a partial replacement of white cement with different ratios of polyurethane foam waste (10%, 20%, 30%, and 40%) based on the weight of cement. The lightweight white cement pastes specimens in addition to conventional white cement paste were cured under tap water for 7 and 28 days. The physical, mechanical, and thermal properties were evaluated. The results showed that the specimens cured for 28 days achieved better properties as compared to the specimens cured for 7 days. Furthermore, at each curing age the specimens of lightweight white cement pastes showed relatively lower properties as compared to the conventional white cement paste and as the polyurethane waste content increased, the properties in terms of compressive strength and bulk density decreased while the total porosity percentage increased especially at higher ratios. On the other hand, the effects of styrene–butadiene rubber latex and irradiation dose on the properties of irradiated polymer impregnated lightweight white cement composites have been investigated. The results confirmed that the impregnation of the hardened lightweight white cement pastes with styrene–butadiene rubber latex and their exposure to different doses of gamma rays (50, 100, 150, and 200 kGy) showed a gradual improvement in the mechanical and physical properties up to 150 kGy and then started to decrease at 200 kGy. Characterization of some selected specimens was carried out by the studying of thermogravimetric analysis, scanning electron microscopy, and X‐ray diffraction. J. VINYL ADDIT. TECHNOL., 25:328–338, 2019. © 2019 Society of Plastics Engineers     

Magnesium sulfate attack on hardened blended cement pastes under different circumstances

This paper describes the sulfate resistance of some hardened blended Portland cement pastes. The blending materials used were silica fume (SF), slag, and calcium carbonate (CaCO₃, CC?). The blended cement pastes were prepared by using W/S ratio of 0.3. The effects of immersion in 10% MgSO₄ solution under different conditions (room temperature, 60 °C, and drying-immersion cycles at 60 °C) on the compressive strength of the various hardened blended cement pastes were studied. Slag and CC? improve the sulfate resistance of ordinary Portland cement (OPC) paste. Mass change of the different mixes immersed in sulfate solution at 60 °C with drying-immersion cycles was determined. The drying-immersion cyclic process at 60 °C accelerates sulfate attacks. This process can be considered an accelerated method to evaluate sulfate resistance of hardened cement pastes, mortars, and concretes.     

不同养护条件下掺循环流化床固硫灰硬化水泥浆的膨胀性能

为探讨掺循环流化床固硫灰(简称固硫灰)硬化水泥浆的体积变化规律,将固硫灰以不同质量取代水泥制备水泥浆试件,结合扫描电子显微镜、压汞仪、X射线衍射仪及TG-DSC同步热分析仪分析了固硫灰及试件的微观形貌、矿物组成和热效应,对三种养护条件下试件的体积膨胀性能进行了试验研究。结果表明：固硫灰的掺入能显著提高浆体标稠用水量,固硫灰掺量80%(质量分数,下同)的浆体标稠用水量是基准组的1.6倍;封闭养护时,硬化浆体体积随固硫灰掺量的增加由收缩(掺量低于40%)变为膨胀(掺量高于60%),且收缩率高于基准组;相较于封闭养护,标准养护使硬化浆体内部水化更充分,大毛细孔含量减少,微观结构更密实,硬化浆体体积膨胀,固硫灰掺量80%的试件28 d膨胀率最高达0.42%;空气养护的试件体积均呈收缩趋势,80%固硫灰掺量的试件水灰比较大,但干燥引起的收缩变形高于膨胀产物产生的膨胀变形。     

The effect of desiccation on the porosity and pore structure of freeze dried hardened portland cement and slag-blended pastes

Mercury porosimetry studies of hardened cement pastes of Portland cement and blast furnace slag blended cements have been conducted after freeze drying cured samples. The samples have been aged after freeze drying in a desiccating atmosphere so as to evaluate the effect of aging on the pore structure of freeze dried hardened Portland cement paste prepared with and without admixtures. Results indicate that after 24 hours of freeze drying the hardened paste shows negligible change in porosity and pore structure with aging in a desiccating atmosphere.     

利用磷石膏制备低热、微膨胀复合水泥的研究

为大量利用磷石膏,本文采用在复合水泥中掺加磷石膏的方法,开展了制备低热、微膨胀复合水泥的试验研究,并采用DSC、XRD、SEM及等温水化热仪表征了该复合水泥的水化特征.研究结果表明:磷石膏具有显著的缓凝效果,通过掺加Na2SO4和提高磷石膏掺量的方法,可大幅度缩短水泥的凝结时间、提高水泥的早期强度.当磷石膏掺量超过10％时,水泥水化产物中钙矾石量显著增加,并出现二水石膏,硬化水泥浆体呈现出微膨胀性.通过调整磷石膏的掺量,可控制复合水泥的膨胀率.     

Effect of curing time on the physicomechanical characteristics of the hardened cement pastes containing limestone

The effect of curing time on the physico-mechanical properties of the hardened Portland cement pastes containing limestone was studied. Five cement-limestone blends were prepared using 0%, 5%, 10%, 15%, and 20% of limestone as a partial substituent of Portland cement. The cement pastes were prepared using the standard water of consistency of 0.255, 0.255, 0.258, 0.261, and 0.263, respectively. The fresh pastes, thus produced, were moulded into 2×2×2-cm cubes. The pastes were first cured within the moulds at 100% relative humidity for 24 h, then the specimens were demoulded and cured under tap water for 3, 7, 14, and 28 days. At each hydration age, the hardened pastes were tested for bulk density, compressive strength, differential scanning calorimetery (DSC), and X-ray diffraction analysis (XRD). The results obtained were related as much as possible to the mechanical properties of the hardened cement pastes. The inclusion of limestone results in a notable improvement of the mechanical properties of the cement pastes containing limestone.     

The influences of siliceous waste on blended cement properties

The influences of siliceous waste on the properties of fly ash and blast furnace slag cement were studied, and its optimum mixing amount in blended cement was determined. The strength, setting time, resistance to chemical attack, dry shrinkage, and impermeability of blended cement mixed with siliceous waste were also investigated by different experiments. The measurement of pore size distribution for hardened cement pastes made by Poremaster-60 was recorded and analyzed in this article.     

水泥熟料与辅助性胶凝材料优化匹配的基础研究进展(Ⅰ)——物理效应

本文分析了复合水泥性能较差的本质原因,并指出优化水泥浆的初始堆积状态和水化进程是改善复合水泥性能的根本途径。在分析经典颗粒堆积模型和水泥颗粒级配模型优缺点的基础上,提出了复合水泥的颗粒级配模型,显著提高了新拌水泥浆体的初始堆积密度(最大固含量提高10%),以改善复合水泥的性能。     

钢渣对硬化水泥浆体结构形成的影响研究

研究了钢渣对水泥强度及体积膨胀率的影响,采用SEM和EDXA分析了水化产物的形貌和微区化学成分,并用XRD对水化产物的矿物组成进行了分析研究。研究结果表明,钢渣的掺入会降低水泥净浆的早期抗压强度,但随钢渣水化的进行,掺钢渣的水泥浆体7d以后的强度增长较快,至120d时净浆抗压强度已与纯硅酸盐水泥相近。掺钢渣的水泥的体积膨胀率比纯硅酸盐水泥的体积膨胀率大,钢渣水泥的体积膨胀率主要取决于钢渣中的fCaO含量。掺钢渣水泥的主要水化产物组成和形貌与纯硅酸盐水泥无明显差别,所不同的是C-S-H凝胶中有较多的铁相。掺钢渣水泥的水化产物主要有C2SH(C)、AFt和Ca(OH)2。     

Physicochemical characteristics of acrylic-acid polymer-impregnated cement pastes

Various Portland cement pastes were made using water cement ratios of 0·20, 0·25, 0·35 or 0·40 and then cured for 1, 3, 7, 28, 90 or 180 days. These pastes were impregnated with acrylic acid monomer under vacuum and the monomer-impregnated samples were then treated at two different temperatures, 40 or 60°C, for the polymerization process, using benzoyl peroxide as initiator. Several physicochemical studies were carried out on each cement paste; these studies include compressive strength tests, bulk density, compressive strength versus gel/space ratio relationships, polymer load, X-ray diffraction analysis and differential thermal analysis. Results have indicated that compressive strength improvement in acrylic acid-polymer impregnated cement pastes is mainly dependent on initial water/cement ratio, curing time and gel/space ratio. The results of X-ray diffraction analysis and differential thermal analysis indicated that the intrusion of polymer into the cement paste matrix does not affect the phase composition of the Portland cement hydration products.     

硫酸盐侵蚀下硬化水泥浆体微结构演变及膨胀过程的数值模拟

根据硫酸盐侵蚀机理,利用改进的CEMHYD3D水化模型和随机概率方法,建立了硫酸盐侵蚀下硬化水泥浆体的微结构演变模型。在微观层次上,模拟了浆体孔溶液中硫酸根离子的自由扩散、随机碰撞和转化反应,分析了膨胀性侵蚀产物生长导致的微结构损伤和体积膨胀,计算了侵蚀过程中石膏和钙矾石的生成量及浆体的膨胀应变,并与已有试验结果对比分析验证了模型的合理性。在此基础上,数值模拟了硫酸盐侵蚀下不同水灰比水泥浆体的微结构演变及膨胀过程。结果表明：同一硫酸盐浓度下,硬化水泥浆体中氢氧化钙和含铝物相与孔隙的接触面积越小,浆体的膨胀应变越低;水灰比为0.25、0.30和0.35的硬化水泥浆体的孔隙填充程度分别达到9.09%、9.27%和9.41%时,浆体膨胀应变开始快速增大;硫酸盐侵蚀溶液浓度增大,浆体体积快速膨胀的时间提前。     

Decalcification shrinkage of cement paste

Decalcification of cement paste in concrete is associated with several modes of chemical degradation including leaching, carbonation and sulfate attack. The primary aim of the current study was to investigate the effects of decalcification under saturated conditions on the dimensional stability of cement paste. Thin (0.8 mm) specimens of tricalcium silicate (C₃S) paste, white portland cement (WPC) paste, and WPC paste blended with 30% silica fume (WPC/30% SF) were decalcified by leaching in concentrated solutions of ammonium nitrate, a method that efficiently removes calcium from the solid while largely preserving silicate and other ions. All pastes were found to shrink significantly and irreversibly as a result of decalcification, particularly when the Ca/Si ratio of the C-S-H gel was reduced below ∼ 1.2. Since this composition coincides with the onset of structural changes in C-S-H such as an increase in silicate polymerization and a local densification into sheet-like morphologies, it is proposed that the observed shrinkage, here called decalcification shrinkage, is due initially to these structural changes in C-S-H at Ca/Si ∼ 1.2 and eventually to the decomposition of C-S-H into silica gel. In agreement with this reasoning, the blended cement paste exhibited greater decalcification shrinkage than the pure cement pastes due to its lower initial Ca/Si ratio for C-S-H gel. The similarities in the mechanisms of decalcification shrinkage and carbonation shrinkage are also discussed.     

A gap-graded particle size distribution for blended cements: Analytical approach and experimental validation

To increase the packing density of blended cement paste, a gap-graded particle size distribution (PSD) was theoretically deduced and modified according to the wet density of actual paste. Then experiments were conducted to validate the hypothesis of improvement of the properties of blended cements by the gap-graded PSDs proposed. The experimental results show that the gap-graded PSD resulted in a decreased water requirement and an increased packing density of blended cement paste, and modified gap-graded PSDs gave further effects. The heat of hydration of gap-graded blended cement pastes released slowly in the first 24 h and increased rapidly afterward. The microstructure of gap-graded blended cements was much more homogeneous and denser than that of reference blended cement, therefore both early and late mechanical properties of low clinker gap-graded blended cements were improved significantly and even higher than those of Portland cement.     

Fracture energy and strength of polymer impregnated cement

The fracture energy, or effective surface energy of hardened cement paste and polymer-impregnated hardened cement paste, was measured by an analytical method. The fracture energy of polymer impregnated hardened cement paste is considerably higher than the unimpregnated past (7.5 × 10⁴ to 0.91 × 10⁴ ergs/cm²). The increase appears to be entirely due to the polymer contribution. The results predict a factor of 5 improvement in the fracture strength of hardened cement paste upon polymer impregnation.     

矿渣、粉煤灰和硅灰对硬化水泥浆体孔隙率的影响

本文用3种不同的试样制备方法和3种测孔方法分别测定了加矿渣、粉煤灰和硅灰等掺合料的硬化水泥浆体孔隙率。结果表明,试样制备方法和孔隙率测定方法一样,都会影响孔隙率的测定结果,掺加掺合料以后,这种影响更为显著。     

The influence of water removal techniques on the composition and microstructure of hardened cement pastes

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.     

Pore solution composition and reinforcement corrosion characteristics of microsilica blended cement concrete

Plain and microsilica blended cement pastes with water-cement ratio of 0.6 were prepared using a 14% C₃A cement. Two levels of chloride from NaCl corresponding to 0.6% and 1.2% by weight of cement were added through mix water. The pastes were allowed to hydrate in sealed containers for 180 days and then subjected to pore solution expression. The expressed pore fluids were analyzed for chloride and hydroxyl ion concentrations. The results show that the OH⁻ ion concentration in the pore solutions of both chloride-free and chloride-bearing pastes drop steeply with increasing cement replacement by microsilica. For 10% microsilica cement pastes the pH for both 0.6% and 1.2% chloride addition was found to be around 13.30. However, the pH drops to a level below that of saturated Ca(OH)₂ solution when cement replacement by microsilica is increased from 10% to 20%. This is ascribable to the consumption of Ca(OH)₂ by microsilica as shown by the DTA/TGA results. 10% and 20% microsilica blending more than doubles the free chloride ion concentration in the pore solutions of the chloride-bearing pastes. 10% microsilica replacement raises the Cl⁻/OH⁻ ratio 4 to 5 fold, whereas for 20% microsilica replacement, the Cl⁻/OH⁻ ratio is increased to 77 and 39 folds over the corresponding values for the plain cement pastes for 0.6% and 1.2% chloride additions respectively. Accelerated corrosion monitoring tests carried out on steel bars embedded in plain and microsilica blended cement concretes exposed to 5% NaCl solution show a 3 fold superior performance of microsilica blended cement concretes in terms of corrosion initiation time. This corrosion behaviour is contrary to the prediction from the increased aggressivity of pore solution composition in terms of highly elevated Cl⁻/OH⁻ ratios. This is attributable to the densification of cement matrix by the pozzolanic reaction between microsilica and calcium hydroxide. No discernable advantage in terms of corrosion initiation time is evident by increasing microsilica blending from 10% to 20%.     

废瓷砖再生骨料对砂浆及砼性能的影响

利用废弃瓷砖制备再生粗、细骨料以取代天然砂石,研究了废瓷砖再生骨料对砂浆、混凝土性能的影响;并通过劈裂实验及抗折实验,对比分析了再生骨料、天然碎石与水泥石的界面粘结性能.结果表明:在相同配比条件下,与天然砂石集料相比,废瓷砖再生骨料有利于提高砂浆、混凝土的强度,减小干缩率,但会导致工作性变差.在相同龄期条件下,不同类型骨料-水泥石的界面粘结强度均随水灰比的降低而增大.在相同水灰比条件下,废瓷砖再生骨料-水泥石界面28 d劈裂强度、抗折强度均较碎石-水泥石界面的要大,表明再生骨料-水泥石界面粘结性能更好.     

沸石粉对硫铝酸盐水泥水化行为的影响机理研究

研究了沸石粉对硫铝酸盐水泥浆体流动度、凝结时间和抗压强度的影响规律,并通过自收缩、电阻率和XRD测试分析了沸石粉在硫铝酸盐水泥水化行为中的作用机理。结果表明,掺入沸石粉后水泥浆体的流动度明显降低,凝结时间显著延长,且延长时间随掺量的增大呈先增大后减小的趋势。当沸石粉掺量为5%~15%(质量分数)时,硬化水泥浆体的1 d、3 d、7 d抗压强度均有显著提高;沸石粉掺量为10%时,水泥浆体3 d、7 d、28 d的强度增长幅度最大,和空白组相比,分别增长了21.6%、13.9%和5.4%。掺入沸石粉后水泥浆体的24 h电阻率显著增大,硬化浆体的7 d自收缩减小,且在相同龄期时,硬化浆体的自收缩随沸石粉掺量的增大而减小。XRD分析显示沸石粉的掺入能有效促进硫铝酸盐水泥的水化,有利于1 d、3 d和28 d龄期内钙矾石的形成。     

How to prepare polished cement product surfaces for optical microscopy without introducing visible cracks

It is shown that preparation procedures may introduce cracks in epoxy impregnated hardened cement paste specimens. This is of vital importance for optical microscopic examination. A method which gives no visible cracks due to preparation is described.