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.     

矿物掺合料对水泥基材料耐海水侵蚀性能的影响研究

加入适当矿物掺合料是使水泥基材料达到高性能的重要手段之一。本课题从工程应用的角度出发,以磨细矿渣和磨细矿渣-粉煤灰复合掺合料为研究对象,着重研究了矿物掺合料对水泥基材料耐海水侵蚀性能的影响。     

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.     

Mechanical and durability performance of sustainable structural concretes: An experimental study

This study reports the results of a wide experimental campaign intended at investigating the mechanical and durability performance of structural concretes made with Recycled Concrete Aggregates (RCAs) and coal Fly Ash (FA). To this end, twelve mixtures were designed by replacing part of the ordinary constituents (i.e. cement, sand and coarse aggregates) of a reference one with RCAs and FA. Samples of these mixtures were subjected to various tests aimed at assessing both their structural properties and durability performance. As for the former, time evolution of compressive strength was monitored at various curing times up to 365 days, and the splitting strength was determined at 28 days. Moreover, the expected durability performance of the aforementioned concrete mixtures was scrutinised by measuring some relevant physical quantities, such as water permeability, carbonation depth and chloride-ions ingress at various curing ages.The results obtained from these tests are often not self-evident, as they unveil the synergistic effect of combining both RCAs and FA on the resulting physical and mechanical properties of “green” concrete. Moreover, they demonstrate that the current code restrictions on the use of both RCAs and FA for structural concrete might be significantly relaxed, especially if the delayed binder effect, induced by the latter, is duly taken into account and, hence, concrete properties are measured at curing times longer than the conventional 28 days.     

Compressive strength and durability properties of ceramic wastes based concrete

This paper presents an experimental study on the properties and on the durability of concrete containing ceramic wastes. Several concrete mixes possessing a target mean compressive strength of 30 MPa were prepared with 20% cement replacement by ceramic powder (W/B = 0.6). A concrete mix with ceramic sand and granite aggregates were also prepared as well as a concrete mix with natural sand and coarse ceramic aggregates (W/B = 0.5). The mechanical and durability performance of ceramic waste based concrete are assessed by means of mechanical tests, water performance, permeability, chloride diffusion and also accelerated aging tests. Results show that concrete with partial cement replacement by ceramic powder although it has minor strength loss possess increase durability performance. Results also shows that concrete mixtures with ceramic aggregates perform better than the control concrete mixtures concerning compressive strength, capillarity water absorption, oxygen permeability and chloride diffusion. The replacement of cement and aggregates in concrete by ceramic wastes will have major environmental benefits.     

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.     

High strength blended cement concrete incorporating volcanic ash: Performance at high temperatures

The strength and durability of high strength blended cement concretes incorporating up to 20% of volcanic ash (VA) subjected to high temperatures up to 800 °C are described. The strength was assessed by unstressed residual compressive strength, while durability was investigated by rapid chloride permeability (RCP), mercury intrusion porosimetry (MIP), differential scanning calorimetry (DSC), crack pattern observations and microhardness testing. High strength volcanic ash concrete (HSVAC) exhibited better performance showing higher residual strength, chloride resistance and resistance against deterioration at high temperatures compared to the control high strength OPC concrete. However, deterioration of both strength and durability of HSVACs increased with the increase of temperature up to 800 °C due to weakened interfacial transition zone (ITZ) between hardened cement paste (hcp) and aggregate and concurrent coarsening of the hcp pore structure. The serviceability assessment of HSVACs after a fire should therefore, be based on both strength and durability considerations.     

Evaluation of Portland limestone cements for use in concrete construction

The paper describes a study carried out to examine the performance of concrete produced using combinations of Portland cement (PC) and limestone (LS), covering compositions for Portland limestone cement (PLC) conforming to BS EN 197-1: 2000, and up to 45% LS. In particular, key engineering (mechanical) and durability properties of concrete were studied. The results indicate only minor differences in performance between PC and 15% PLC concretes of the same cement content and water/cement (w/c) ratio (cement = Portland cement + addition). However, there was an adverse effect with increasing LS content beyond 15% of the cement content for many properties. It is shown that for 35 N/mm² cube strength concrete the adjustment to w/c ratio to match the compressive strength of PC concrete was in the region of 0.08 for each 10% LS added (water curing at 20°C) above this level. Studies of permeation and concrete durability performance, including, initial surface absorption, carbonation resistance, chloride diffusion, freeze/thaw scaling and abrasion resistance, indicate that in general the test concretes followed single relationships with strength for most properties. Consideration is given to the practical implications of the main outcomes of the study.     

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.     

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.     

Use of spent foundry sand and fly ash for the development of green self-consolidating concrete

In the United States alone, the foundry industry discards up to 10 million tons of sand each year, offering up a plentiful potential resource to replace sand in concrete products. However, because the use of spent foundry sand (SFS) is currently very limited in the concrete industry, this study investigates whether SFS can successfully be used as a sand replacement material in cost-effective, green, self-consolidating concrete (SCC). In the study, SCC mixtures were developed to be even more inexpensive and environmentally friendly by incorporating Portland cement with fly ash (FA). Tests done on SCC mixtures to determine fresh properties (slump flow diameter, slump flow time, V-funnel flow time, yield stress, and relative viscosity), compressive strength, drying shrinkage and transport properties (rapid chloride permeability and volume of permeable pores) show that replacing up to 100% of sand with SFS and up to 70% Portland cement with FA enables the manufacture of green, lower cost SCC mixtures with proper fresh, mechanical and durability properties. The beneficial effects of FA compensate for some possible detrimental effects of SFS.     

A study on reinforcement corrosion and related properties of plain and blended cement concretes under different curing conditions

This paper presents the results of an experimental investigation on the steel reinforcement corrosion, electrical resistivity, and compressive strength of concretes. Concretes having two different water–cement ratios (0.65 and 0.45) and two different cement contents (300 and 400 kg/m³) were produced by using a plain and four different blended portland cements. Concrete specimens were subjected to three different curing procedures (uncontrolled, controlled, and wet curing). The effect of using plain or blended cements on the resistance of concrete against damage caused by corrosion of the embedded reinforcement has been investigated using an accelerated impressed voltage setup. The resistivity of the cover concrete has been measured non-destructively by placing electrodes on concrete surface. The compressive strength, electrical resistivity, and corrosion resistance of the concretes were determined at different ages up to 180 days. The results of the tests indicated that the wet curing was essential to achieve higher strength and durability characteristics for both plain and especially blended cement concretes. The concretes, which received inadequate (uncontrolled) curing, exhibited poor performance in terms of strength and corrosion resistance.     

Durability assessment of alkali activated slag (AAS) concrete

The environmental impact from the production of cement has prompted research into the development of concretes using 100% replacement materials activated by alkali solutions. This paper reports research into the durability of AAS concrete. The durability properties of AAS have been studied for a range of sodium oxide dosages and activator modulus. Properties investigated have included measurements of workability, compressive strength, water sorptivity, depth of carbonation and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. It was concluded that an activator modulus of between 1.0 and 1.25 was identified as providing the optimum performance for a sodium oxide dosage of 5% and that AAS concretes can exhibit comparable strength to concrete currently produced using Portland cement (PC) and blended cements. However, with regards to the durability properties such as water sorptivity, chloride and carbonation resistance; the AAS concretes exhibited lower durability properties than PC and blended concretes. This, in part, can be attributed to surface microcracking in the AAS concretes.     

Particle size effect on the strength of rice husk ash blended gap-graded Portland cement concrete

Rice husk ash (RHA) has been used as a highly reactive pozzolanic material to improve the microstructure of the interfacial transition zone (ITZ) between the cement paste and the aggregate in high-performance concrete. Mechanical experiments of RHA blended Portland cement concretes revealed that in addition to the pozzolanic reactivity of RHA (chemical aspect), the particle grading (physical aspect) of cement and RHA mixtures also exerted significant influences on the blending efficiency. The relative strength increase (relative to the concrete made with plain cement, expressed in %) is higher for coarser cement. The gap-grading phenomenon is expected to be the underlying mechanism. This issue is also approached by computer simulation. A stereological spacing parameter (i.e., mean free spacing between mixture particles) is associated with the global strength of the blended model cement concretes. This paper presents results of a combined mechanical and computer simulation study on the effects of particle size ranges involved in RHA-blended Portland cement on compressive strength of gap-graded concrete in the high strength/high performance range. The simulation results demonstrate that the favourable results for coarser cement (i.e., the gap-graded binder) reflect improved particle packing structure accompanied by a decrease in porosity and particularly in particle spacing.     

Performance of metakaolin concrete at elevated temperatures

An experimental investigation was conducted to evaluate the performance of metakaolin (MK) concrete at elevated temperatures up to 800 °C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chloride-ion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200 °C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents.     

Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag

In order to reduce energy consumption and CO₂ emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements. Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC, PLC, and PC cements on fresh properties (such as slump flow diameter, T ₅₀₀ slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production considerably enhanced the fresh characteristics of SCCs.     

Durability characteristics of self-consolidating concrete designated for repair applications

This paper presents test results carried out to study the influence of key mixture parameters on frost durability, scaling resistance, and transport properties of self-consolidating concrete (SCC) that can be used in structural repair. Regardless of the w/cm, binder type, or admixture combination, properly designed SCC can develop high resistance to freezing and thawing with frost durability factor greater than 80%. The optimized mixtures had 56-day rapid chloride-ion permeability (RCP) values of 200–900 Coulomb. On the average, SCC made with 0.42 w/cm developed 20% higher capillary porosity, 20% lower compressive strength, and 30% greater RCP value compared to similar SCC prepared with 0.35 w/cm. The type of blended cement in use had considerable influence on transport properties. For a given mix design, concrete with 180 mm slump consistency exhibited similar RCP value of 505 Coulomb compared to 630 Coulomb for the same concrete with greater dosage of HRWRA to secure a slump flow consistency of 670 mm.     

Fluid transport in high volume fly ash mixtures with and without internal curing

The transport of fluid and ions in concrete mixtures is central to many aspects of concrete deterioration. As a result, transport properties are frequently measured as an indication of the durability that a concrete mixture may be expected to have. This paper is the second in a series investigating the performance of high volume fly ash (HVFA) mixtures with low water-to-cementitious ratios (w/cm) that are internally cured. While the first paper focused on strength and shrinkage, this paper presents the evaluation of the transport properties of these mixtures. Specifically, the paper presents results from: rapid chloride migration (RCM), rapid chloride penetration test (RCPT), apparent chloride diffusion coefficient, surface electrical resistivity, and water absorption. The test matrix consisted of mortar samples with two levels of class C fly ash replacement (40% and 60% by volume) with and without internal curing provided with pre-wetted lightweight fine aggregates (LWA). These mixtures are compared to plain ordinary portland cement (OPC) mortars. The results indicate that HVFA mixtures with and without internal curing provide benefits in terms of reduced transport coefficients compared to the OPC mixtures.     

Effects of deicers on the performance of concrete pavements containing air-cooled blast furnace slag and supplementary cementitious materials

This study investigates the effects of continuous deicer exposure on the performance of pavement concretes. For this purpose, the differences in the compressive strength, the changes in the dynamic modulus of elasticity (DME) and the depth of chloride ingress were evaluated during and after the exposure period. Eight different concrete mixtures containing two types of coarse aggregates (i.e. air-cooled blast furnace slag (ACBFS) and natural dolomite) and four types of binder systems (i.e. plain Type I ordinary portland cement (OPC) and three combinations of OPC with fly ash (FA) and/or slag cement (SC)) were examined. These mixtures were exposed to three types of deicers (i.e. MgCl₂, CaCl₂, and NaCl) combined with two different exposure conditions (i.e. freezing-thawing (FT) and wetting-drying (WD)). In cold climates, these exposure conditions are the primary durability challenges that promote the physical deterioration of concrete pavements. The results indicated that among the studied deicers, CaCl₂ had the most destructive effect on the tested concretes while NaCl was found to promote the deepest level of chloride ingress yet was shown to have the least damaging impact on concretes. The microstructure evaluation revealed that the mechanism of concrete deterioration due to the deicer exposure involved chemical reactions between the deicers and concrete hydration products. The use of FA or SC as partial replacements for OPC can offset the detrimental effects of both deicers and FT/WD cycles.