An investigation on the recycling of hydrated cement from concrete demolition waste

Construction and demolition waste (CDW) recycling is generally limited to the use of the coarser fraction as aggregate for new concrete. The recovery of fine aggregates requires a cleaning by removing the hydrated cement waste (HCW). In this paper, the possibility to use HCW extracted from CDW as alternative component for the production of new clinker is explored.A pure HCW sample was prepared and used in partial replacement of natural materials in raw admixtures for new clinker production. At a replacement degree of 30%, a new Portland clinker containing almost 50% of C₃S could be produced with a huge spare in the release of CO₂ (about 1/3 less). At higher HCW dosage a non-Portland clinker containing almost 80% of C₂S has been obtained: its use as supplementary cementing material in blended cements revealed satisfying long term performances.     

Influence of dispersing agents on the rheology and early heat of hydration of blended cements with high loading of calcined marl

The dispersing effectiveness of five commercial plasticizers; lignosulfonate (LS), naphthalene sulphonate–formaldehyde polycondensate (NSF) and three polycarboxylate ethers (PCEs) were quantitatively investigated in blended cements where ordinary Portland cement (OPC) was partly replaced by calcined marl (CM) up to 60%. CM drastically viscosified and decreased the flow of the cement due to high absorption of water. The performance of plasticizers mimics that in the OPC system except when PCEs were added. PCEs possessing long side chains were less effective as dispersants due to the consumption of these polymers via the ability of their PEO side chains to intercalate between the remaining layers in the calcined clay. Higher dosages were thus needed for effective dispersion. The decrease in PCE–OPC interaction led to little retardation in cement hydration except at high polymer dosages, whereas the performance of NSF and LS in CM blended cement is driven by clinker content.     

Effects of sandblasting distance and angles on resin cement bonding to zirconia and titanium

ObjectivesThe aim of this study was to evaluate effects of sandblasting distance and angles resin to zirconia and titanium bonding.MethodsDensely sintered zirconia and cp2 titanium specimens were prepared and randomly divided into groups, and then sandblasted with various distance (5 mm, 10 mm and 15 mm) and angles (45°, 60°, 75° and 90°). After surface treatment, each specimen surface underwent a silane primer application (RelyX, 3M ESPE), followed by bonding of a resin cement (RelyX Unicem Aplicap, 3M ESPE). Then, each cylindrical resin stub (diameter 3.6 mm×2 mm) underwent a shear adhesive (bond) strength test and surface roughness evaluation. SEM evaluation and EDX analysis were used to observe surface properties of both zirconia and titanium samples. Results were statistically analyzed using analysis of variance (ANOVA) and Turkey test (α=0.05).ResultsSurface roughness showed a significant difference amongst the different distances and angles for both the zirconia and titanium materials and these changes in surface roughness were evident in the SEM imaging photos. As for the adhesive strength, there was a significant difference in the adhesive strength for the titanium and zirconia with different angles. In general, 75° gives the best results although this is not significantly different from 90°. However, no significant difference was observed in changes of sandblasting distance for both materials. EDX analysis at the surface revealed elements carbon, oxygen, silicon, aluminum, and zirconia on the surface.ConclusionsSandblasting at various distance and angles contributes differences in surface roughness when it comes to both zirconia and titanium materials. Despite both 75° or 90° sandblasting angle could yield a sufficiently high adhesive strength for resin to titanium or zirconia bonding, sandblasting at 75° seems to be optimal to increase the adhesive strength.     

Glass waste as supplementary cementing materials: The effects of glass chemical composition

Sustainable cements containing 25 wt% of different types of recycled glass have been investigated as a supplementary cementing material in order to highlight the role of glass chemical composition during the hardening process. Glass formers, stabilizers and modifiers regulate the glass dissolution in the alkaline environment during cement hydration. As a consequence, pozzolanic reaction and/or alkali–silica reaction are strictly related to the glass chemical composition. The mechanical and microstructure characterizations of mortar samples containing glass blended cements and un-reactive aggregates allow to determine which oxides in the glass have to be carefully monitored to avoid deleterious reactions.     

空气炮在解决水泥库出库溜子堵塞中的应用

针对水泥库结块经常堵塞下料溜子的问题,决定在溜子处安装空气炮,将空气炮压缩空气出口稍微上扬,以便于击打堵在下料口的结块。经实际使用,效果良好,改善了生产环境,降低了员工的劳动强度。     

耐火预制件在水泥窑中的应用

耐火预制件是将不定形耐火材料定形化，兼具有定形和不定形的优点。本文针对耐火预制件的特点以及在原料配比、形状设计等方面的要求，根据水泥窑不同部位的使用条件，分别介绍了篦冷机矮墙及顶部预制件、三次风管弯道预制件、三次风管闸板预制件、窑头罩预制件，为水泥窑用耐火材料的长寿化提供了方法，具有良好的应用前景。     

Investigating multicomponent breakage in cement grinding

The production of blended cements involves grinding raw materials such as cement clinker, pozzolan, blast furnace slag, limestone and gypsum, within the same mill. This is known as intergrinding. However, it is not possible to control the product fineness of each component separately in the multicomponent system and this results in overgrinding of relatively softer components. Since each component exhibits different breakage characteristics, the fineness of the components around the closed grinding circuit will vary depending on relative grindabilities and the overall fineness of the cement will then depend on the ratio of the components in the blend with different grindabilities. This paper aims to examine the size by mass distribution of each component around a closed circuit ball mill during cement production by intergrinding. For this purpose, a ball mill with an air classifier in a cement plant was sampled and size by assay analyses of the samples was carried out to calculate the particle size distribution of each component around the circuit. The results indicated that the size distributions of the components in each stream vary depending on their grindabilities and the final product comprises components with different fineness. The breakage rates of the components were calculated and it was seen that the breakage rates of the relatively softer components are higher than that of harder ones.     

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

The effect of microencapsulated phase-change materials (MPCM) on the rheological properties of pre-set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s⁻¹. New empirical equations were developed to quantify the time-dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D-geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear-induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.     

水泥辊压机终粉磨系统的工业化应用

介绍了水泥辊压机终粉磨系统及运行情况,与辊压机联合粉磨系统生产的水泥以及所配制的混凝土进行了对比,水泥辊压机终粉磨系统电耗大幅降低,两种水泥所配制的混凝土性能相当。     

Effect of nonionic side chain length of polycarboxylate-ether-based high-range water-reducing admixture on properties of cementitious systems

Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures, most previous reports on the cement-admixture compatibility did not provide sufficient information on the structure of the admixture. Hence, the evaluation and generalization of the reports on the cement-admixture compatibility are challenging. In this study, three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content, anionic/nonionic molar ratio, and main chain length and different side chain lengths were produced. The compatibility of these admixtures with a CEM I 42.5R-type cement was investigated. In addition, an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type, admixture/cement ratio, and elapsing time to the Marsh funnel flow time, mini-slump, slump flow, and compressive strength. The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems. However, the admixture having the shortest side chain was better with regard to flow retention. The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures. Regarding the behaviors of the admixtures in the cementitious systems, an optimal admixture side chain molecular weight is proposed.