Efficiency of internal curing by superabsorbent polymers (SAP) in PC-GGBS mortars

This paper evaluates the effect of superabsorbent polymers (SAP) on hydration and microstructure of PC-GGBS mortars. Development of autogenous shrinkage, microstructural characteristics (MIP/SEM) and compressive strength were analysed during the first 90 days. Four levels of Portland cement (PC) replacement by GGBS (0%, 25%, 50% and 75%) and two types of SAP with different water absorption capacities were considered. The results proved the efficiency of internal curing by SAPs in PC-GGBS systems due to significant reduction in autogenous shrinkage, especially for higher contents of GGBS. SAP facilitates GGBS hydration activated by portlandite; its products can be deposited into the nano pores leading to a small relative expansion of the hardened bulk volume. This process is initiated during the second week and it lasts until the sixth week. Despite increased total porosity, compressive strength of SAPs modified mortars is comparable to the reference samples for low GGBS contents in advanced ages.     

Binary and ternary effects of ground dune sand and blast furnace slag on the compressive strength of mortar

The aim of this study is to promote the use of available natural dune sand from desert areas as a partial cement replacement. Binary and ternary combinations of ground dune sand (GDS), Portland cement (PC) and ground granulated blast furnace slag (GGBS) were investigated for their effects on the compressive strength of mortar cured under standard or autoclave curing conditions. The results showed that the compressive strength decreased significantly with increasing GDS and GGBS contents under standard curing. However, with autoclave curing, all of the binary and ternary mixtures yielded mortar with a compressive strength higher than that of the control sample. The autoclave-cured ternary combination of 30% GDS, 50% PC and 20% GGBS showed the highest compressive strength. It is possible to use a PC content as low as 10% since the mixture of 30% GDS, 10% PC and 60% GGBS displayed strength comparable to the control sample.     

Plastic shrinkage cracking of concrete incorporating mineral admixtures and its mitigation

In recent years, there has been a rapid increase in the use of mineral admixtures for high performance and durable concrete. Plastic shrinkage cracking in such concretes is a serious concern in large surface area/volume applications. The present study has two objectives: firstly, to investigate the influence of incorporating fly ash and granulated blast furnace slag (GGBS) on the susceptibility to such cracking; and secondly, to assess the techniques, such as fibre and shrinkage reducing admixture (SRA) addition, and spraying of curing compounds, to mitigate the cracking. The results indicate that replacement of ordinary Portland cement (OPC) with fly ash and GGBS increases the possibility of plastic shrinkage cracking significantly, with higher severity as the replacement level increases; 30% replacement of OPC with fly ash and GGBS doubled and quadrupled the crack area, respectively, mainly due to higher binder finesses, and the delay of setting and strength gain. Among the fibres tested, polypropylene and polyester fibres, at the recommended dosages of about 0.9 kg/m³, completely eliminated cracking in the most affected concrete (i.e., with 30% GGBS) while the dosages of the polyacrylonitrile and glass fibres had to be increased to provide a higher volume fraction. Two glycol-based SRAs, and two curing compounds based on acrylic resin and methacrylate mitigated cracking by significantly reducing evaporation from the surface of concrete.     

Rice husk ash as both pozzolanic admixture and internal curing agent in ultra-high performance concrete

The present study investigated the effects of mesoporous amorphous rice husk ash (RHA) on compressive strength, portlandite content, autogenous shrinkage and internal relative humidity (RH) of ultra-high performance concretes (UHPCs) with and without ground granulated blast-furnace slag (GGBS) under different treatments. The results were compared with those of UHPCs containing silica fume (SF). Because of the mesoporous structure, RHA can absorb an amount of aqueous phase to decrease the free water content and to supply thereafter water for further hydrations of cementitious materials. Hence, compressive strength of RHA-blended samples is enhanced. The highly water absorbing RHA delays and slows down the decrease in the internal RH (self-desiccation) of UHPCs, and hence strongly mitigates autogenous shrinkage of UHPCs compared to SF. The combination of GGBS and RHA or SF improves the properties of UHPC. These results suggest that RHA acts as both highly pozzolanic admixture and internal curing agent in UHPC.     

Mechanical and cementitious characteristics of ground granulated blast furnace slag and basic oxygen furnace slag blended mortar

Reusing waste materials and reducing carbon emissions are crucial environmental concerns. Ground granulated basic oxygen furnace slag (GGBOS) and ground granulated blast furnace slag (GGBS) are the by-products of the steel industry and has positive effects on the environment because it reduces the problems associated waste disposal. This study reused these two products to completely replace cementitious materials, thus contributing to waste recycling, reducing the production demand for cement, and mitigating carbon emissions. Twelve mixture proportions were designed in this study, including an ordinary Portland mortar (OPM) as the control group and 11 steel/iron slag blended mortar (SISBM) experimental groups for the mechanical and cementitious characteristic experiments. The optimal mixing ratio for SISBM compressive strength ranged from GGBOS (steel slag): GGBS (iron slag) = 3:7 to 5:5 (by weight). At the age of 91 days, the compressive strength of SISBM reached 80–90% compared with that of the control group. Based on the pH values, free-CaO, and microanalysis results, the cementitious characteristics were mainly generated because the GGBOS increased the free-CaO or Ca(OH)₂ concentrations in the SISBM curing water and provided alkaline environments for Ca(OH)₂ to engage in the pozzolanic reaction with the SiO₂ and Al₂O₃ in GGBS, forming crystals such as calcium aluminum silicate hydrate, (C–A–S–H), calcium silicate hydrate (C–S–H), and calcium–magnesium–alumina–silicate (C–M–A–S), which generated strength and strengthened microstructure.     

Specifying concrete for chloride environments using controlled permeability formwork

The paper describes a study carried out to explore how controlled permeability formwork (CPF) can be used within existing concrete durability specifications (mix limitations) for chloride environments. Tests were carried out to consider (i) chloride diffusion rates and, under wetting and drying conditions, (ii) rates of chloride contamination build up at cover depth and (iii) reinforcement corrosion. The effects of CPF were measured against design strength, cover depth and cement type of concrete cast against ply-wood formwork (impermeable formwork—IMF). The use of CPF liner on formwork was found to significantly enhance chloride and corrosion resistance of concrete. Moreover, the results demonstrated that CPF could be used within the BS 5328 durability framework for chloride environments to allow either a 20 mm cover reduction (50 to 30 mm) at fixed design strength (40 N/mm²), or a reduction in design strength of 10 N/mm² (50 to 40 N/mm²) at fixed cover depth (30 mm). It was additionally found for Portland cement (PC) concrete that the use of CPF gave equivalent performance to concretes containing PFA and GGBS as constituents of cement and a ternary cement comprising both materials, cast against ply-wood formwork. This suggests that the ‘trade offs’ within BS 8500 for PC/PFA and PC/GGBS cements in chloride environments, could also be permitted for CPF concrete containing PC.     

Properties of concrete incorporating fly ash and ground granulated blast-furnace slag

This paper presents a laboratory study on the influence of combination of fly ash (FA) and ground granulated blast-furnace slag (GGBS) on the properties of high-strength concrete. A contrast study was carried out for the concrete (GGFAC) incorporating FA and GGBS, control Portland cement concrete and high-volume FA high-strength concrete (HFAC). Assessments of the concrete mixes were based on short- and long-term performance of concrete. These included compressive strength and resistance to H₂SO₄ attack. The microstructure of the concretes at the age of 7 days and 360 days was also studied by using scanning electron microscope. The results show that the combination of FA and GGBS can improve both short- and long-term properties of concrete, while HFAC requires a relatively longer time to get its beneficial effect.     

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.     

An experimental study on optimum usage of GGBS for the compressive strength of concrete

This paper presents a laboratory investigation on optimum level of ground granulated blast-furnace slag (GGBS) on the compressive strength of concrete. GGBS was added according to the partial replacement method in all mixtures. A total of 32 mixtures were prepared in four groups according to their binder content. Eight mixes were prepared as control mixtures with 175, 210, 245 and 280 kg/m³ cement content in order to calculate the Bolomey and Féret coefficients (K_B, K_F). For each group 175, 210, 245 and 280 kg/m³ dosages were determined as initial dosages, which were obtained by removing 30 percent of the cement content of control concretes with 250, 300, 350, and 400 kg/m³ dosages. Test concretes were obtained by adding GGBS to concretes in an amount equivalent to approximately 0%, 15%, 30%, 50%, 70%, 90% and 110% of cement contents of control concretes with 250, 300, 350 and 400 kg/m³ dosages. All specimens were moist cured for 7, 14, 28, 63, 119, 180 and 365 days before compressive strength testing.The test results proved that the compressive strength of concrete mixtures containing GGBS increases as the amount of GGBS increase. After an optimum point, at around 55% of the total binder content, the addition of GGBS does not improve the compressive strength. This can be explained by the presence of unreacted GGBS, acting as a filler material in the paste.     

Preparation of Ultra-High Performance Concrete with common technology and materials

The technology development of concrete and demand for high strength construction materials give momentum to the development of Ultra-High Performance Concrete (UHPC). Current UHPC preparation methods require costly materials and relatively sophisticated technology. To overcome these weaknesses, this paper focused on the preparation of UHPC with common technology and ordinary raw materials. Influence of binder content, water/binder ratio, ground granulated blastfurnace slag (GGBS) content, and limestone powder (LP) replacement on fluidity and compressive strength of concrete were researched, respectively. The test results show that the addition of superplasticizer and fine mineral additives enabled the UHPC to be produced at an extremely low water/binder ratio of 0.14-0.18, achieving excellent workability with a maximum slump of 268 mm and compressive strengths of 175.8 MPa at 90 d and 182.9 MPa at 365 d.     

Durability performance potential and strength of blended Portland limestone cement concrete

This paper describes a study on the durability potential and strength of composite Portland-limestone cement (PLC) concrete mixtures blended with ground granulated blast furnace slag (GGBS) and/or fly ash (FA). Their performance was compared against ordinary Portland cement, plain PLC and Portland-slag cement concrete mixtures. Using the South African Durability Index approach, results indicate reductions in the penetrability of the composite PLC blends compared to the other mixtures. The durability indicators are chloride conductivity, gas (oxygen) permeability and water sorptivity. Compressive strength of the composite PLC mixtures containing both GGBS and FA showed competitive performance with the comparative mixtures, but FA blended PLC mixtures had diminished compressive strength values. The paper also presents considerations on the practical implications of using blended PLC concrete mixtures.     

A site study of durability indexes for concrete in marine conditions

The paper describes an investigation into the validity of durability index tests when used in a site situation and to evaluate the effectiveness of site curing methods. Concretes manufactured and cured under site conditions in a warm, humid coastal environment were investigated using recently developed durability index tests.Three blended binders (GGBS, FA and CSF) were used to cast a series of wall and slab elements. The elements were cured using practical site methods currently employed in the industry. Cores were extracted at early (28-day) and later (120-day) ages and used to determine the durability index properties.The results indicated that it is possible to manufacture, place and cure site concrete to achieve acceptable durability properties. Full wet curing proved to be the most effective method, as expected. While variation in potential durability properties existed at early age (28 days) between site and wet cured samples, at a later age (120 days) the variations had reduced such that, in practical and general terms, the different site curing methods were virtually indistinguishable. It was clear that environmental curing continues after 28 days provided climatic conditions are conducive for this to occur. Thus, on-going environmental curing largely governs the potential durability. To develop a concrete durability performance specification, it is imperative that a system is developed to quantify the effects of the environment on potential durability.     

Feasible use of large volumes of GGBS in 100% recycled glass architectural mortar

The use of 100% recycled glass as aggregates in architectural mortar is regarded as an environmentally friendly, cost-effective and attractive feature for construction applications due to the natural characteristics of glass (e.g. aesthetic pleasing, impermeability, chemical resistance properties). However, the need to use large quantities of white cement for architectural products may increase the overall cost of production. Therefore, the possibility of using a near-white coloured ground granulated blast furnace slag (GGBS) to replace white cement for architectural mortar production is an attractive option. This paper reports a study which is an extension of our previous work aiming to investigate the feasibility of using large volumes of GGBS (ranging from 15% to 75% white cement replacements) to produce self-compacting-based architectural mortars. To improve the appearance (whiteness) of the mortar, a small quantity of titanium dioxide (TiO₂) was added to the selected mixes for comparison purposes. Fresh and hardened properties of the mortar including mini-slump flow, density, water absorption, flexural strength, equivalent compressive strength, drying shrinkage, alkali silica reaction (ASR) and acid attack resistance were investigated. The overall performance showed that it is feasible to use GGBS for the production of architectural mortar and 60% replacement of white cement by GGBS was determined to be optimal. The replacement significantly increased the flexural strength, and reduced the drying shrinkage and risk of ASR expansion, as well as improved the ability to resist acid attack of the mortar produced.     

Limestone addition effects on concrete porosity

The effect on porosity (including absorption and sorpitivity) of cement paste and mortar/concrete, of limestone addition to Portland cement is assessed. Based on globally sourced literature published in English since 1993, consisting of 171 publications from 35 countries. The data analysed were from wide ranging tests. The effect on pore structure was also examined in terms of type of Portland cement and limestone, cement fineness and method of producing it, curing, maturity and water-cement ratio, as well as the cement composites with fly ash, slag (GGBS), silica fume and metakaolin and related to strength. Overall, it is suggested that though the use of limestone up to 25% with Portland cement should not impair the pore structure, limit on limestone content for its effect on strength is likely to be about 15%. This should be considered where higher proportion of limestone content is allowed in the Standards.     

PDLC based on unsaturated polyester resins: molecular, morphological and thermo-optical analysis

A thermosetting matrix based on an unsaturated polyester resin was employed to realise a Polymer Dispersed Liquid Crystal (PDLC) system by a UV induced curing process. A molecular, morphological and thermo-optical characterisation of this system is presented. The chemical and structural properties were investigated by transmission FT-IR spectra in the near infrared frequency range and by dynamic-mechanical analysis. The results indicated that, upon curing, the matrix retains its intrinsic properties even for compositions very rich in the LC component (40 wt %). The morphology, investigated by optical and electron microscopy, showed phase separation before and after the curing process. Image analysis demonstrated that the cured materials had morphological features suitable to achieve interesting thermo-optical properties. In particular, the composition containing 40 wt % of LC exhibited the typical behaviour of a thermo-optical switch. Interesting optical bistability effects were also demonstrated for this particular composition.     

Efficiency of ground granulated blast-furnace slag replacement in ceramic waste aggregate mortar

From our previous findings, the recycling of ceramic waste aggregate (CWA) in mortar has been proved an ecological means plus an excellent outcome against chloride ingress. The CWAs were porcelain insulator wastes supplied from an electric power company, which were crushed and ground to fine aggregate sizes. In this study, to further develop the CWA mortar as an eco-efficient construction material, ground granulated blast-furnace slag (GGBS) was incorporated. The slag (having the Blaine fineness of 6230 cm²/g) was utilized as a supplementary cementitious material (SCM) at three different replacement levels of 15%, 30%, and 45% of cement by weight. The efficiency of the GGBS on enhancing chloride resistance in the CWA mortars was experimentally assessed by using a silver nitrate solution spray method and an electron probe microanalysis (EPMA). The tests were carried out on mortar samples after immersed in a 5.0% NaCl solution for 24 weeks. Another set of the mortar samples was exposed to a laboratory ambient condition for 24 weeks and then followed with a carbonation test. The test results indicated that the resistance to the chloride ingress of the CWA mortar becomes more effective in proportion to the replacement level of the GGBS. In contrast, the carbonation depth of the CWA mortar increases with the increase of the GGBS. The activeness of the GGBS was also evaluated on the basis of the compressive strength development up to 91 days. Due to its high fineness, the GGBS can be used up to 30% while the high relative strength (more than 1.0) is achieved at all ages.     

空心玻璃微珠/环氧树脂固体浮力材料模压成型工艺及性能

借鉴陶瓷材料模压成型工艺提出了适用于环氧树脂基固体浮力材料制备的真空辅助模压成型自由固化方法，实现了固体浮力材料制备过程中成型与固化环节的分离，为高性能固体浮力材料的制备提供了新方法。以环氧树脂(E-4221)为基体，空心玻璃微珠(Hollow glass microsphere, HGMS)做填充材料，采用模压成型自由固化方法制备高HGMS体积分数的HGMS/E-4221固体浮力材料，研究了HGMS体积分数、成型压力对HGMS/E-4221固体浮力材料密度、抗压强度、吸水率等性能的影响。结果表明，真空辅助模压成型自由固化方法适用于HGMS体积分数为65%~67%的HGMS/E-4221固体浮力材料制备，所获得的HGMS/E-4221固体浮力材料密度为0.621~0.655 g/cm3，适用深度可达到8 000~10 000 m。      

Blended cements—Applications and implications

The paper aims to emphasise that the practical aspects of producing and using concretes made from blended cements is equally important as research and development work on these materials when considering the long-term durability aspects of structures in which they form part.

The manufacture of the base materials is given, as are a number of factors to appreciate when producing and using concretes made from PFA, GGBS and MS. Also presented is a summary of durability benefits which can be gained through a full appreciation of the properties of the concretes in both fresh and hard states.

An introduction of quality management systems for these products concludes the paper.     

热残余应力对内埋光纤光栅传感器性能的影响

将布拉格光纤光栅(FBG)埋植于复合材料T型加筋板结构非干涉区—三角填充区作为应变传感器对复合材料加筋板在固化过程及冲击后压缩过程中的应变变化进行监测。对比了光纤刻栅区采用UV光固化树脂涂层保护和未保护的两种FBG传感器的波谱信号变化; 分析了复合材料在固化成型过程中产生的非轴对称热残余应力对FBG传感性能的影响。结果表明, 刻栅区采用聚合物涂层保护的FBG传感器的半峰宽(FWHM)在固化过程中未发生变化, 并且聚合物涂层可以有效地消除非轴对称热残余应力对光纤光栅反射波谱的影响。在冲击后压缩过程中, 采用聚合物涂层保护的FBG传感器测得的应变与贴于试样表面的应变片测得的应变数据一致性较好。本文对埋植于复合材料加筋板三角填充区的FBG传感器在复合材料固化过程及冲击后压缩过程中应变监测的有效性及可靠性进行了有益的探索。     

Characterisation of high-performance cold bitumen emulsion mixtures for surface courses

Cold bitumen emulsion mixture (CBEM) is not yet widely used as a surface course around the world. In this study, 0/14-mm-size dense-graded surface course CBEMs have been investigated. The mechanical performance was evaluated in terms of stiffness modulus over 3 months and resistance to permanent deformation under three different stress levels (100, 200, 300 kPa), whilst durability evaluation was carried out in terms of resistance to moisture and frost damage. The study has also investigated the incorporation of low cement content (1%) with relatively sustainable by-product fillers, namely ground-granulated blast furnace slag (GGBS) and fly ash (FA) type 450-S on both mechanical and durability performance. A comparison has been carried out between the low and high cement content CBEM, as well as with respect to corresponding hot mix asphalt (HMA). The results revealed that the incorporation of GGBS and FA in CBEMs leads to superior performance, similar to CBEMs treated with high cement content and comparable to an equivalent HMA. Furthermore, GGBS replacement exhibited better performance than that of FA replacement. The findings suggest that the new sustainable types of CBEM can be developed for using as a surface layer for medium- to heavy-trafficked roads.