Development of alpha plaster from phosphogypsum for cementitious binders

Efforts have been made to make high strength alpha plaster from phosphogypsum, a by-product of phosphoric acid industry. Phosphogypsum was autoclaved in slurry form (phosphogypsum 50% + water 50%, by wt.) in the laboratory at different steam pressures for different durations in presence of chemical admixtures. It was found that with small quantity of chemical admixture (sodium succinate/potassium citrate/sodium sulphate), alpha plaster of high strength can be produced. The optimum pressure and duration of autoclaving was found to be as 35 psi and 2.0 h, respectively. The alpha plaster was examined for making cementitious binders by admixing hydrated lime, fly ash, granulated blast furnace slag, marble dust and chemical additives with alpha plaster. Data showed that cementitious binder of compressive strength of 22.0 and 30 MPa (at 28 days of curing at 40° and 50 °C) and low water absorption was produced. DTA and SEM studies of the binder showed formation of CSH, ettringite and C₄AH₁₃ as main cementitious products to give strength.     

Calcium sulfate hemihydrate activated low heat sulfate resistant cement

Investigations were undertaken to produce low heat sulfate resistant cement by activation of granulated slag obtained from the blast furnace process of iron making and phosphate industries with the calcium sulfate hemihydrate. Experimental data showed that cement gives fast setting characteristics in addition to high strength development. The setting time of cement was regulated with a small addition of set retarder without adversely affecting the strength development of cement. It is noted that beta hemihydrate plaster gives better strength results than the anhydrite activated cement. The results also confirm that granulated blast furnace slag can be replaced with phosphatic slag up to 10% by mass without loosing strength. DTA and X-ray diffraction analysis have been used to identify the hydration products formed in the hydrated cement. The heat of hydration data of cement is reported in the paper.     

磷石膏制备复相磷石膏煅烧工艺研究

对磷石膏制备的复相石膏煅烧工艺进行了研究。结果表明:保温时间和升温速率对两种石膏的烧成比例影响较大。获得不同半水-无水比例的复相磷石膏体系可以通过控制升温速率和保温时间来实现。复相磷石膏与单相石膏比较,具有较好的早期强度和后期强度。     

Structural,physical and mechanical properties of modified wood–magnesia composite

The results of research about the structural, physical and mechanical properties of wood–magnesia composites based on magnesium binder (caustic magnesia) and filler of wood sawdust modified with chemical industry waste fluorine anhydrite (fluoranhydrite) are described. It was found that during the hydration of caustic magnesia containing fluorine anhydrite additive in composition with magnesium chloride, magnesium oxychlorides with different morphologies are formed depending on the initial components. The structure examination after 9 years of products maintenance showed the intensive carbonization of caustic magnesia hydration products with the formation of magnesium hydroxycarbonates that caused the increase of the material density, strength, water resistance and decrease of the wood–magnesia constructional beam creeping deformations.     

Environment hazard mitigation of waste gypsum and chalk: Use in construction materials

The rapid urbanization and industrialization have resulted in the production of various types of solid, liquid and gaseous wastes which pose serious problems to the environment. The disposal and use of solid industrial wastes like phosphogypsum, fluorogypsum, fly ash, slag, and lime sludge, is significant in view of their availability and potential applications. The paper deals with studies on select wastes like phosphogypsum and chalk for use in value-added building materials. The engineering properties and techno-economics of materials like gypsum plasters, cementitious binders, boards/blocks, masonry cement and flooring tiles produced from phosphogypsum and lime have been detailed. The production and use of building materials from such wastes will protect the environment from degradation.     

磷石膏在矿渣-偏高岭土地聚合物中的应用

本文对磷石膏在矿渣-偏高岭土中的应用进行了研究。通过SEM、EDX、XRD、化学结合水研究了其水化产物与微观形貌,并测试了地聚合物的抗折、抗压强度。结果表明,矿渣-偏高岭土地聚合物的水化产物主要为无定形态的C-(A)-S-H或N-(A)-S-H,加入磷石膏后,体系中生成了晶态的钙矾石。当磷石膏掺量达到20%后,硬化浆体具有较高的化学结合水增长速率,且抗压强度显著高于对照组。     

Extending internal curing to concrete mixtures with W/C higher than 0.42

Internal curing (IC) is an effective method for improving performance of low W/C – low permeability concretes because they require additional water to hydrate the cementitious materials. Conventional concretes, on the other hand, contain enough water to hydrate the cementitious materials, but are frequently not properly cured, allowing drying and compromising strength gain and durability. The aim of this investigation is to assess the effect of IC as a complement to traditional curing in relatively high W/C concretes (W/C above 0.42) under drying conditions. Degree of hydration, compressive strength, and permeability were measured in concretes with IC and without IC. Results show that even under drying conditions, mixtures with IC exhibit 16% higher hydration, 19% higher compressive strength, and 30% lower permeability than their counterparts with no IC. This suggests that IC can be very useful for improving performance in concrete mixtures with relatively high W/C under poor curing conditions.     

Role of phosphogypsum impurities on strength and microstructure of selenite plaster

The effect of phosphatic, fluoride and organic impurities as present in waste phosphogypsum were studied on the setting time, strength development and microstructure of the selenite gypsum plaster. The results showed that these impurities affect the physical properties of the plaster in a similar fashion as observed in the setting and hardening of the phosphogypsum plaster. The selenite plaster sets fast with a fall in strength. The selenite plaster which normally crystallizes into long interlocking needle shaped crystals has been found to be modified to prismatic, lath, and tabular shaped crystals of variable sizes interspersed with radiating crystals and anhedral to subhedral microcrystallites having irregular boundaries and poor stacking. It is concluded that formation of prismatic and lath-like crystal of different morphology affect the normal setting and strength characteristics of selenite gypsum plaster to a great extent. The effect is more pronounced when soluble phosphatic, fluoride and organic matter were added to the selenite plaster than the sparingly and less soluble compounds intermixed.     

Autoclaved brick from low-silicon tailings

The load-bearing brick is made from low-silicon tailings by pressing and autoclaving process, in the presence of alkali-activated slag/fly ash cementing material (AAFSC). Tailings accounts for 83% of the total mass of the brick. The compressive strength of the brick is up to 16.1 MPa, bending strength 3.8 MPa, and with low drying shrinkage and good freeze–thaw resistance. Some factors influencing the mechanical strength of the brick including forming pressure, forming water content and curing regime, are investigated. The hydration products, freeze–thaw durability and anti-carbonation characteristics of the products are discussed.     

碱激发矿渣粉煤灰混凝土性能研究

碱矿渣水泥与混凝土具有硬化快、强度高、水化热低、孔结构良好、抗渗性及抗冻性好、抗化学侵蚀能力强等一系列的物理力学性能和耐久性能。本文使用水玻璃作为主要碱组分,同时应用大量矿渣和粉煤灰,配制出了强度高、耐久性优良的碱激发矿渣粉煤灰混凝土。     

化学预处理对磷石膏基复合胶凝材料性能的影响

研究了不同液固比和不同溶液浓度的化学预处理方式对磷石膏pH值、残余磷含量、磷石膏基复合胶凝材料凝结时间和力学性能的影响,进一步分析了预处理方式对磷石膏基复合胶凝材料水化产物物相组成及微观形貌的影响.结果表明:磷石膏的pH值与预处理溶液的液固比呈二次函数递增关系,与溶液浓度呈线性函数递增关系;溶液液固比的增加能降低残余磷含量,但溶液浓度的增加会抑制磷的去除;碱溶液预处理通过增加磷石膏的pH值来产生促凝效应,去离子水或自来水预处理通过减少残余磷含量来减弱缓凝效应;预处理能促进水化反应的进行,加速早期钙矾石的生成,缩短凝结时间,提高早期强度.     

Investigation on phosphogypsum–steel slag–granulated blast-furnace slag–limestone cement

This study investigated a cementitious material by utilizing two industrial wastes, phosphogypsum (PG) and steel slag (SS), combined with another industrial byproduct ground granulated blast-furnace slag (GGBFS) and limestone (LS). The 28d compressive strength of a mixture of 45% PG, 10% SS, 35% GGBFS and 10% LS exceeded 40 MPa. XRD and SEM analyses showed that the main hydration products were ettringite and C–S–H gel. Part of PG reacted with GGBFS and SS to form ettringite, the residual PG was wrapped by hydration products. SS in the cement acted as an alkalinity activator. Over dosage of SS may cause unsoundness.     

MMA化学灌浆材料的研究及其在土木工程中的应用

本文叙述了细微裂隙固结和补强灌浆材料的设计,MMA化学灌浆材料的特点,及其应用效果。MMA化学灌浆材料具有粘度比水低,能在-19～-23℃硬化,硬化后不收缩,强度高,粘结能力强,耐老化,浆液毒性低,硬化后不污染环境,施灌工艺简单等优点。用于基岩固结灌浆,能使弱风化岩体的参数提高到微风化或新鲜岩体的水平;用于混凝土裂缝补强灌浆,能恢复混凝土的整体性。     

Durability of soft clay soil stabilized with recycled Bassanite and furnace cement mixtures

This study examines the wetting–drying durability of soft clay soil stabilized with recycled Bassanite, produced from gypsum waste. Specifically, this study focuses on an investigation of the effects of the moisture conditions on the strength performance and durability of very soft clay soil stabilized with Bassanite and furnace cement mixtures during the wetting–drying cycles, referred to as weathering conditions in this study. Cylindrical stabilized soil specimens were produced and then cured for 28 days. The cured specimens were subjected to different numbers of wetting–drying cycles, and then tested for unconfined compressive strength. The results show that the compressive strength increased with an increase in the Bassanite content for the different wetting–drying cycles investigated. The increase in the Bassanite content is associated with the increase in the dry unit weight, as well as in the decrease in the moisture content of the stabilized specimens for the different wetting–drying cycles investigated. The compressive strength of the soil stabilized with the Bassanite and furnace cement mixtures gradually decreases with an increase in the number of wetting–drying cycles, and the earlier cycles are seen to have a more negative effect on durability than the later cycles. Generally, the influence of the wetting–drying cycles on changes in the strength, durability and volume of the soft clay soil stabilized with Bassanite and furnace cement mixtures is not significant. This is evidence that the use of recycled Bassanite, produced from gypsum waste to stabilize soft clay soil, achieves acceptable durability, raises the strength performance and improves the engineering properties of soft clay soil in a wet environment. In addition, the effective use of gypsum waste contributes to the development of a sustainable society by reducing the huge quantity of solid waste and establishing a sound environment.     

Basic properties of non-sintering cement using phosphogypsum and waste lime as activator

This study aims to manufacture non-sintering cement (NSC) by adding phosphogypsum (PG) and waste lime (WL) to granulated blast-furnace slag (GBFS) as sulfate and alkali activators. The non-sintering cement’s basic physical and chemical properties are also investigated by evaluating the compressive strength, and the hydrate of NSC. As a result, although the compressive strength is fairly similar to that of ordinary Portland cement (OPC) in the early curing age, it reaches a higher level in the later age than that of OPC due to the continuous reaction of slag and PG. Results obtained from analysis of the hydrate have shown that the glassy films of GBFS are destroyed by the activation of alkali and sulfate, ions eluted from the inside of GBFS react with PG and produce ettringite, and consequently the remaining component in GBFS slowly produced C–S–H(I) gel. Here, PG is considered not only to play the role of simple activator, but also to work as a binder reacting with GBFS.     

Durability of cementing binders based on fly ash and other wastes

The paper deals with the cementitious binders produced by blending 60–70% fly ash with fluorogypsum, hydrated lime sludge, with and without Portland cement and chemical activator in different proportions. Data show that strength development of cementitious binders takes place through formation of ettringite, C–S–H and wollastonite compounds. The durability of these binder has been studied by its performance in water and by accelerated aging i.e. alternate wetting and drying as well as by heating and cooling cycles at temperatures in the range 27–50 °C. The results indicate Lawrence of strength of binder with the increasing cyclic studies at different temperatures. The maximum fall in compressive strength was noticed at 50 °C.     

竹炭对粉煤灰陶瓷砖结构及性能的影响

采用粉煤灰、黄金尾矿为主要原料,添加不同掺量的竹炭,通过干压成型-高温烧成法制得粉煤灰陶瓷砖,分析了竹炭掺量及烧成温度对粉煤灰陶瓷砖的物化性能、物相组成及显微结构的影响规律.结果表明:以粉煤灰、黄金尾矿和竹炭可以制备出显气孔率和强度较高、吸水率较低的粉煤灰陶瓷砖,其物相主要为石英相与莫来石相;在m(竹炭):m(粉煤灰)为5:70,烧成温度为1 250℃时,陶瓷砖具有较好的综合性能,其破坏强度可达600.1 N,吸水率为8.29%,显气孔率为16.02%,达到GB/T 4100—2006附录K中对BⅡ类炻质砖的性能要求,且该材料的比表面积为11.1 m~2/g,具备一定的吸附功能,有望成为一种新型的内墙功能装饰材料.     

Prognose der Dauerhaftigkeit mineralischer Außenputze mit Hilfe von beschleunigten Alterungstests

Predicting the durability of mineral external plaster using accelerated ageing tests. This article presents a technique for accelerated ageing tests for different plasters. Two models were developed for describing the durability. The models describe changes in selected characteristics due to frost damage and leaching. The first model is based on changes in mass, the second on changes in strength. The models consider the main characteristics that influence durability, such as strength, porosity, permeability, adhesive tensil strength and aggressive environmental influences. Both models enable the durability of external plaster to be predicted.     

含竹炭黄金尾矿陶瓷砖制备研究

采用黄金尾矿、紫金土为主要原料,添加不同配比的竹炭,通过干压成型-高温烧成法制备含竹炭黄金尾矿陶瓷砖,分析了竹炭添加量与烧成温度对陶瓷砖的物化性能、物相组成及显微结构的影响规律.研究结果表明,黄金尾矿、紫金土和竹炭的复合可以制备强度较高、吸水率较低的陶瓷砖,其物相主要为石英,显微结构呈规则网络状;在竹炭/黄金尾矿质量比为5/70,烧成温度为1125℃时,陶瓷砖具有较好的综合性能,其破坏强度可达528.9N,吸水率0.04%,达到GB/T4100-2006<陶质砖>附录L中对BⅢ类陶质砖破坏强度的要求,有望成为一种新型的环境友好型陶瓷砖.     

Carbon nanotube–cement composites: A retrospect

Although ordinary Portland cement (OPC) is widely used in the construction industry, its weak tensile strength, to some extent, limits its application. A carbon nanotube (CNT), on the other hand, has outstanding mechanical properties with a tensile strength of 63 GPa and Young's modulus of 1 TPa, making it a candidate as nano-scale reinforcements in OPC. Past research studies have reported improved mechanical and electrical properties of carbonnanotube–ordinary Portland cement (CNT–OPC) composites, which show future promise in practical civilengineering applications. In this study, recent research studies in developing CNT–OPC composites are comprehensively reviewed. Highlighted herein are the considerable efforts been made in the study of fabrication, hydration, porosity and transport properties of the CNT–OPC composites. There are, however, future investigations needed to provide a better understanding in the areas of uniform dispersion of CNTs within the OPC paste, durability, impact, fatigue properties and the theoretical modelling of CNT–OPC interaction.