Effect of ground fly ash and ground bagasse ash on the durability of recycled aggregate concrete

This research aims to study the effect of ground fly ash (GFA) and ground bagasse ash (GBA) on the durability of recycled aggregate concrete. Recycled aggregate concrete was produced with recycled aggregate to fully replace crushed limestone in the mix proportion of conventional concrete (CON) and GFA and GBA were used to partially replace Portland cement type I at the rate of 20%, 35%, and 50% by weight of binder. Compressive strength, water permeability, chloride penetration depth, and expansion by sulfate attack on concretes were investigated.The results reveal that the use of GFA and GBA to partially replace cement in recycled aggregate concrete was highly effective in improving the durability of recycled aggregate concrete. The suitable replacement of GFA or GBA in recycled aggregate concrete to obtain the suitable compressive strength, low water permeability, high chloride penetration resistance, and high sulfate resistance is 20% by weight of binder.     

Studies on mechanics of development of physical and mechanical properties of high-volume fly ash-cement pastes

High-volume fly ash concrete for structural applications was developed at CANMET. In this concrete fly ash to ‘total cementitious material’ was maintained over 55%. The purpose of this work was to investigate, by the use of similar paste mixtures of the same fly ash and cement, the mechanism by which the mechanical properties were developed. Mechanical property-porosity relations, pore size distribution, permeability, degree of hydration and Ca(OH)₂ content measurements were made. It was observed that the fly ash-cememt reaction occurred relatively early at 3 to 7 days and it was concluded that the cement matrix and residual unreacted fly ash form a good mechanical bond.     

Transport properties of high volume fly ash roller compacted concrete

This paper describes research on the transport properties of high-volume fly ash roller compacted concrete (RCC). The mixes were developed through incorporating 50–260 kg/m³ cement and high volumes of fly ash ranging from 40% to 85% by mass of the total cementitious material. The concretes were investigated for permeability, absorption, sorption and chloride diffusion. The study showed that RCCs of moderate cement and moderate fly ash contents had lower values of permeability, absorption, sorption and chloride diffusivity.     

The interfacial zone and bond strength between aggregates and cement pastes incorporating high volumes of fly ash

The weak transition zone between aggregate and cement paste controls many important properties of concrete. A number of studies dealing with interfacial zone are available in the literature for normal concrete and concrete containing silica fume. High-volume fly ash concrete for structural applications was developed at CANMET in the 1980s, but to date there has been no information available for interfacial zone in high-volume fly ash concrete.In this paper, the orientation index and mean size of Ca(OH)₂ crystals in the aggregate-paste interfacial zone were determined by the X-ray diffractometer. The bond strength between the aggregate and paste was also investigated. It was found that, at the age of 28 days, there was no obvious transition zone between the aggregate and cement paste incorporating high volumes of fly ash. The higher the paste strength, the higher is the bond strength.     

Effect of mix design inputs,curing and compressive strength on the durability of Na2SO4-activated high volume fly ash concretes

This paper aims to advance research on the use in concrete of a high volume of fly ash, with a high loss on ignition value, aiding in sustainable low carbon footprint construction. To this end, the work explores the benefits that may be achieved in terms of long-term concrete performance from the incorporation of fly ash along with a chemical activator. Durability tests are performed on concrete with an activated hybrid cementitious system: Portland cement (PC) and high volume fly ash with sodium sulfate. The chloride diffusion coefficient significantly decreased over time for the activated system (50% PC - 50% fly ash with added sodium sulfate) compared to the control samples (100% PC and 80% PC - 20% fly ash) at the same water to cementitious material ratio. This behavior is particularly evident in samples cured under controlled laboratory conditions (100% RH and 23 °C). However, outdoor curing increases the permeability for all concretes. Long term carbonation is also investigated under natural exposure conditions, and samples that are cured outdoors exhibit a significant carbonation depth. The compressive strength is correlated with the durability parameters: the durability performance improves as the compressive strength increases, indicating that as is the case for Portland cement (but not always for alkali-activated binders), the microstructural factors which yield high strength are also contributing to durability properties.     

Correlation between compressive strength and certain durability indices of plain and blended cement concretes

In this study, plain, silica fume and fly ash cement concrete specimens prepared with varying water to cementitious materials ratio and cementitious materials content were tested for compressive strength, water permeability, chloride permeability, and coefficient of chloride diffusion after 28 days of water curing. The data so developed were statistically analyzed to develop correlations between the compressive strength and the selected durability indices of concrete. Very good correlations were noted between the compressive strength and the selected durability indices, particularly chloride permeability and coefficient of chloride diffusion, irrespective of the mix design parameters. However, these correlations were observed to be dependent on the type of cement.     

Influence of a fine glass powder on the durability characteristics of concrete and its comparison to fly ash

A detailed investigation carried out to ascertain the durability characteristics of fine glass powder modified concretes is reported in this paper. Tests were designed to facilitate comparisons between concretes modified with either glass powder or fly ash at the same cement replacement level. The optimal replacement level of cement by glass powder is determined from strength and hydration tests as 10%. The later age compressive strengths of glass powder and fly ash modified concretes are seen to differ by only 5%. The durability characteristics are ascertained using tests for rapid chloride permeability, alkali–silica reactivity, and moisture transport parameters. The chloride penetrability values indicate some amount of pore refinement. The potential of glass powder to reduce the expansion due to alkali–silica reaction is established from tests conducted in accordance with ASTM C 1260, but fly ash is found to perform better at similar replacement levels. Glass powder–fly ash blends that make up a 20% cement replacement level are found to be as efficient as 20% fly ash in reducing expansion. The control concrete is seen to exhibit the lowest overall moisture intake after 14 days of curing, and fly ash concrete the highest, with the glass powder concrete in between. The trend is reversed at later ages, demonstrating that both the replacement materials contribute to improved durability characteristics. The sorptivity and moisture diffusion coefficient values calculated from the moisture intake-time data also demonstrate a similar trend. These studies show that fine glass powder has the potential to improve the durability of concretes.     

Durability aspect of concretes composed of cold bonded and sintered fly ash lightweight aggregates

This study reports the finding of an experimental study carried out on the durability related properties of the lightweight concretes (LWCs) including either cold bonded (CB) or sintered (S) fly ash aggregates. CB aggregate was produced with cold bonding pelletization of class F fly ash (FA) and Portland cement (PC) while S aggregate was produced by sintering the fresh aggregate pellets manufactured from FA and bentonite (BN). Two concrete series with water-to-binder (w/b) ratios of 0.35 and 0.55 were designed. Moreover, silica fume (SF) with 10% replacement level was also utilized for the purpose of comparing the performances of LWCs with and without ultrafine SF. The durability properties of concretes composed of CB and S aggregates were evaluated in terms of water sorptivity, rapid chloride ion permeability, gas permeability, and accelerated corrosion testing after 28 days of water curing period. The compressive strength test was also applied to observe the strength level at the same age. The results revealed that S aggregate containing LWCs had relatively better performance than LWCs with CB aggregates. Moreover, the incorporation of SF provided further enhancement in permeability and corrosion resistance of the concretes.     

Use of natural zeolite as a supplementary cementitious material

Natural zeolite, a type of frame-structured hydrated aluminosilicate mineral, is used abundantly as a type of natural pozzolanic material in some regions of the world. In this work, the effectiveness of a locally quarried zeolite in enhancing mechanical and durability properties of concrete is evaluated and is also compared with other pozzolanic admixtures. The experimental tests included three parts: In the first part, the pozzolanic reactivity of natural zeolite and silica fume were examined by a thermogravimetric method. In this case, the results indicated that natural zeolite was not as reactive as silica fume but it showed a good pozzolanic reactivity. In the second part, zeolite and silica fume were substituted for cement in different proportions in concrete mixtures, and several physical and durability tests of concrete were performed. These experimental tests included slump, compressive strength, water absorption, oxygen permeability, chloride diffusion, and electrical resistivity of concrete. Based on these results, the performance of concretes containing different contents of zeolite improved and even were comparable to or better than that of concretes prepared with silica fume replacements in some cases. Finally, a comparative study on effect of zeolite and fly ash on limiting ASR expansion of mortar was performed according to ASTM C 1260 and ASTM C 1567. Expansion tests on mortar prisms showed that zeolite is as effective as fly ash to prevent deleterious expansion due to ASR.     

Concrete durability presented by acceptable chloride level and chloride diffusion coefficient in concrete: 10-year results in marine site

Generally, concrete with high resistance to the marine environment should have high compressive strength, a low chloride diffusion coefficient (D _C), and a high acceptable chloride level (Ac). Considering all parameters simultaneously, this study evaluated the degree of fly ash concrete durability based on 10-year results in a marine site. Based on the concrete durability (Ac/D _C, as compared to cement concrete with a W/B ratio of 0.45) and compressive strength, the degree of concrete durability proposed in this study indicates that fly ash concretes with a W/B ratio of 0.45 and 15–35 wt % fly ash replacement exhibit high-quality performance in a marine site.     

Service life and global warming potential of chloride exposed concrete with high volumes of fly ash

Today, it remains unclear how ‘green’ concrete with high volumes of fly ash really is, especially when subject to chloride-induced corrosion. This paper presents chloride diffusion test results for high-volume fly ash and fly ash + silica fume concrete. Apparent diffusion coefficients and surface concentrations were compared with those for traditional concrete. Instantaneous chloride diffusion coefficients and ageing exponents were estimated and critical chloride contents for submerged exposure conditions were experimentally verified. The estimated time to chloride-induced steel depassivation for the two concrete types with fly ash (60 to more than 100 years) was much longer than for traditional concrete (24–32 years). As a consequence, global warming potentials (GWPs) calculated for the required concrete volume per unit of strength and service life indicate that an important reduction in greenhouse gas emissions is possible for both concrete types with high volumes of fly ash (GWP –50 to −82%).     

Influence of cement type on ITZ porosity and chloride resistance of self-compacting concrete

With the increasing use of self-compacting concrete (SCC) its durability has come into focus. Concerning the microstructure of concrete, the porosity in the interfacial transition zone (ITZ) is regarded as a key feature for permeability and durability. Generally, a combination of cement and mineral admixtures is used for the production of SCC. In the present study, ITZ porosity of four SCC mixtures produced with ordinary Portland cement, Portland limestone cement, slag cement and ordinary Portland cement combined with fly ash is analyzed. Additionally, the chloride migration coefficient is determined. ITZ porosity and width of the SCC mixtures are similar. The substantial differences in the chloride migration coefficients show that the binder type has a stronger influence on permeability than the pore volume in the ITZ.     

Strength and durability properties of polyester concrete using pet and fly ash wastes

Recycled poly(ethylene terephthalate), PET, mainly recovered from plastic beverage bottles, can be used to produce unsaturated polyester resins. In turn, these resins can be mixed with inorganic aggregates (sand and gravel and fly ash waste), to produce polyester concrete (PC). The strength and durability properties of plain and steel-reinforced polyester concrete (PC) using unsaturated polyester resins based on recycled PET and fly ash fillers are discussed in this paper. The recycling of PET and fly ash in PC helps in reducing the cost of the material and alleviating an environmental problem posed by waste materials. The material may effectively be used in many construction applications such as utility, transportation and building components, and the repair and overlay of pavements, bridges and dams.     

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.     

Transport properties of self compacting concrete with limestone filler or fly ash

The durability of a cementitious material is greatly influenced by the permeability of the material for potentially aggressive substances. As the pore structure of self compacting concrete (SCC) might be different in comparison with traditional concrete (TC), some changes in durability behaviour may occur. At this moment however, it is unclear how significant these differences will be with regard to the concrete practice. In this paper, the gas and water transport in SCC with limestone filler or fly ash is investigated experimentally. Nine different concrete compositions are considered: one TC and eight SCC mixtures. Some important parameters like the water/cement (W/C) and cement/powder ratio (C/P), type of filler (limestone filler and fly ash), type of aggregate and type of cement are considered. The results of the gas and water transport are discussed and linked to experimental data concerning pore volume. Lower transport properties can be obtained by using fly ash instead of limestone as filler material, by lowering the W/C ratio, decreasing the C/P ratio at a constant W/C ratio or using blast furnace slag cement instead of portland cement. The effect of changing from gravel to crushed limestone is small. SCC is differing strongly of TC with respect to the apparent gas permeability. This difference is probably due to the differences in pore volume, as seen from MIP results.     

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.     

Use of a high-calcium fly ash in blended type cement production

Eighty percent of fly ash produced by Greek Public Power Corporation (PPC) is of a high-calcium variety. It has a low insoluble residue and a high content in CaO as well as in SO₃. It also shows self-cementing properties. About 20% of it is used by cement companies in blended type cement production.

In this paper mechanical strengths and some other characteristics concerning blended cement and concrete made with it are presented. Special difficulties anticipated in using such a marginal fly ash in cement are also mentioned.     

高性能道面混凝土抗冻耐久性研究与应用

针对传统的普通道面混凝土施工和易性不易控制、强度储备偏低、道面表面品质差、耐久性不良等现象,通过掺加粉煤灰、引气剂、减水剂等外掺剂配制高性能道面混凝土。室内试验和现场应用效果均表明：与普通道面混凝土相比较,掺粉煤灰、引气减水剂的高性能道面混凝土施工方便,匀质性好,强度和抗冻性能均有显著提高。建议在严寒、寒冷地区修建的机场道面工程应大力推广应用掺外掺剂的高性能混凝土。     

Influence of recycled aggregate on slump and bleeding of fresh concrete

The recycling of construction and demolition (C&;D) waste as a source of aggregates for the production of new concrete has attracted increasing interests from the construction industry. While the environmental benefits of using recycled aggregates are well accepted, some unsolved problems prevent this type of material from wide application in structural concrete. One of the major problems with the use of recycled aggregates in structural concrete is their high water absorption capacity which leads to difficulties in controlling the properties of fresh concrete and consequently influences the strength and durability of hardened concrete. This paper presents an experimental study on the properties of fresh concrete prepared with recycled aggregates. Concrete mixes with a target compressive strength of 35 MPa are prepared with the use of recycled aggregates at the levels from 0 to 100% of the total coarse aggregate. The influence of recycled aggregate on the slump and bleeding are investigated. The effect of delaying the starting time of bleeding tests and the effect of using fly ash on the bleeding of concrete are explored.