Comparison of ground waste glass with other supplementary cementitious materials

Finely ground glass has pozzolanic properties that make attractive its recycling as supplementary cementitious material. This paper compares the behaviour of waste glass powders of different fineness with that of natural pozzolana, coal fly ash and silica fume. Chemical analysis, compressive strength measurements and durability tests were carried out to investigate the effect of ground glass on strength and durability performances of mortars. Blended both with Portland cement and lime, ground glass improved strength, resistance to chloride penetration and resistance to sulphate attack of mortars more than natural pozzolana and similarly to fly ash. Mortars with ground glass immersed in water for seven years did not show any sign of degradation and increased their compressive strength. The ranking of ground glass with respect to the other mineral additions was not affected by fineness.     

Effect of rice-husk ash on durability of cementitious materials

In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated. Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied. The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The results were compared with those of cementitious materials without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction. The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material.     

Pozzolanic cements

Natural and artificial pozzolanas have been used to obtain hydraulic binders for over a thousand years. Hardening of pozzolanic cement pastes can result from the reaction between pozzolana and the lime that is added to the mix as hydrated lime or is produced following hydration of portland cement silicates. The pozzolanic reaction does not alter cement clinker hydration; it complements and integrates the hydration process because it results in a lower portlandite content and an increase in calcium silicate hydrates.

Besides reviewing the most recent investigations on pozzolana-containing cements, this paper shows that the behaviour of different types of pozzolana can be quite similar when they are blended and become hydrated along with portland cement clinker. Portland cement properties may undergo several qualitative modifications the extent of which substantially depends on the pozzolana/clinker ratio. So, a maximum is reached in pozzolanic cements.

As in the case of pozzolanic cements, for which the current pozzolana content is about one third by weight of cement, the most outstanding variations induced in the behaviour of portland cement can be summarised as follows. Heat of hydration decreases whilst the rate of clinker hydration increases, paste porosity increases and permeability decreases, both portlandite content and Ca/Si ratio in C-S-H decrease and the C-S-H content increases.

Chemical and physical properties of pozzolanic cements eventually affect engineering ones. Early strength of both pastes and concretes decreases while ultimate strength is often found to exceed that of the reference portland cement.

If cements contain small amounts of very active pozzolana (silica fume, for example), both early and ultimate strengths may be higher than those of the substituted cement.

Creep is found to increase definitely with increasing pozzolana content whereas shrinkage remains practically unaffected.

Chemical and microstructural variations in the paste also influence resistance of concretes to environmental attacks.

The low basicity and permeability resulting from the presence of pozzolana increase the concrete's resistance to lime leaching, sulphate and sea water attacks, and chloride penetration. Carbonation depth is practically unaffected. Pozzolana containing cements can help avoid expansion induced by alkali-silica reaction. Concrete resistance to freezing is not affected by the use of pozzolanic cement since it basically depends on the entrained air content.

The results of a variety of studies introducing a comparison between pozzolana-containing cements and corresponding portland cements can be summarised as follows: cements with appreciable pozzolana contents perform better in the long term rather than at an early age.

In most cases, however, the differences between the two types of cements are not so marked and as a consequence both cements are interchangeable especially for the most common building types.     

Performance and leaching analysis of a novel coal sludge-based backfill material

In this article, an innovative backfill material is introduced as a green material largely utilizing two major coal mining waste: coal refuse and coal sludge. Coal refuse is rock-like solid waste, comparatively, raw coal sludge is slurry. A smart recipe design of backfill material was introduced, which contains only 1 % of cement and the rest 99 % of raw material is from industry waste. The backfill material at 75 % pulp density shows excellent performance such as high unconfined compressive strength, great flowability, and low bleeding rate. Also, the article discusses the morphology change of the backfill harden body during different curing ages, the observation through SEM–EDS illustrates the distinguished morphological characterization of the needle-like ettringite and amorphous gel. Furthermore, TCLP results indicate that this designed backfill material is environmentally acceptable and none of the heavy metal leaching has over the limitation by US Environmental Protection Agency (EPA).     

Thermal activation on calcium silicate slag from high-alumina fly ash: a technical report

The fly ash with alumina composition from 45 to 55 % has been found in China in last 10 years, which attracts great attention from Chinese government and related alumina industry. Chinese government and its state-owned enterprises have successfully extracted the Al as alloy product from the high-alumina fly ash. However, to recycle the calcium silicate slag as residue from the Al industry is still undetermined. In this report, an innovative process is introduced to achieve the regional sustainability for the high-alumina fly ash industry, and it is found that the cementitious material composed of calcium silicate slag met with the mechanical requirements of 32.5 cement for road pavement. The chemical and mineral analysis show that the calcium silicate slag has high CaO content, which reaches up to 48.64 %. C₂S and C₃A are the dominant mineral phases by XRD analysis indicating its potential pozzolanic activity during the hydration process. Thermal activation from 200 to 900 °C was applied to enhance its pozzolanic activity for the calcium silicate slag and it proved that 600 °C is the optimal calcination temperature due to the decomposition of calcite and clay minerals. Also the mineral phase amorphization was also observed during the XRD analysis, which might also contribute to the enhanced pozzolanic properties at 600 °C. Although the designed cementitious material contains a large quantity of solid waste, none of the hazardous heavy metals exceed the EPA limits. This short article originally reported a promising direction for managing solid waste for Al industry and enhancing utilization efficiency for the enterprise internal solid wastes.     

Mechanical and durability properties of cement mortar with Algerian natural pozzolana

This paper presents a study of the properties and behaviour of cement mortar with natural pozzolana from Algeria. The effect of level of addition of natural pozzolana (0, 10, 20, 30, and 40%) on the mechanical properties of mortars at different ages as well as the effect of curing environment and the period of initial curing on the mechanical properties were investigated. The performance of natural pozzolana cement exposed to three aggressive solutions (acids, sulphate, and chloride) is also analysed. The results indicate that the strength of pozzolanic cement is lower than that of plain Portland cement at early ages, but can reach the same order of strength at longer curing periods. The enhancement of the resistance to acid and sulphate attack as well as to chloride ion penetration of natural pozzolanic cement is also demonstrated.     

Influence of pozzolana on sulfate attack of cement stone affected by chloride ions

This study investigated the influence of natural pozzolana (opoka) additive on the hydration of Portland cement and the effects of pozzolana on sulfate attack of cement stone affected by chloride ions. In the samples, 25 % (by weight) of the Portland cement was replaced with pozzolana. The specimens were hardened for 28 days in water, and then one batch was soaked in a saturated NaCl solution and another in a 5 % Na₂SO₄ solution for 3 months at 20 °C. After being kept for 3 months in a saturated NaCl solution, samples were transferred to a 5 % Na₂SO₄ solution and kept under these conditions for 3 months. It was estimated that under normal conditions, pozzolana additive accelerated the hydration of calcium silicates and initiated the formation of CO₃ ^2?–AFm; opoka also decreased the threshold pore diameter of hardened Portland cement paste. It was found that Cl^– ions penetrate to monosulfoaluminate, form Friedel’s salt, and release SO₄ ^2? ions, which react with unaffected monosulfoaluminate and form extra ettringite; when samples were transferred to the 5 % Na₂SO₄ solution, a greater quantity of new ettringite was formed. Meanwhile, pozzolana additive reduced the penetration of chloride and sulfate ions into the structure of Portland cement hydrates and inhibited sulfate attack of cement stone treated in a saturated NaCl solution.     

Effect of W/B ratios on pozzolanic reaction of biomass ashes in Portland cement matrix

In this study, the effects of W/B ratios on pozzolanic reaction of by-product biomass ashes, namely rice husk-bark ash (RHBA) and palm oil fuel ash (POFA), were determined. These biomass ashes were ground to the same fineness as that of Type I Portland cement (OPC) and partially replaced OPC at replacement levels of 10-40% by weight of binder. Water to binder (W/B) ratios of 0.50, 0.575, and 0.65 were used. The compressive strengths of mortars were compared to those of mortars made with OPC partially replaced with ground river sand of similar particle size. The results demonstrate that at the same cement replacement levels, the degrees of pozzolanic reaction of RHBA and POFA increase with W/B ratio. In addition, ground river sand with the same particle size of OPC can be used as a non-reactive material to replace OPC for determining the compressive strength due to pozzolanic reaction of biomass ash.     

Microwave dielectric heating to disassemble a modified cementitious joint

According to existing theory on the deterioration of cement and concrete, a cement hardener undergoes a hydrate disassembly reaction at high temperatures of 300 °C or above; this increases the internal void volume and decreases the residual strength. This weakness mechanism has already been applied to manufacturing recycled aggregates and has reached the stage of practical application for removing adhered mortar from the aggregate surface. However, heating using an external heat source consumes a considerable amount of energy, and greenhouse gases are emitted during the recycling process because of low energy efficiency. In this study, a susceptor with outstanding microwave heating efficiency was selected, and the temperature elevation characteristics from the microwave heating of cementitious material containing the susceptor were analyzed. Through measurement, the bond strength of a cementitious joint including a modifier with the susceptor was found to weaken after microwave heating; thus, a new cementitious joint that can be reused or recycled as construction material and members is proposed. If the susceptor can selectively make cement material vulnerable in a short time by absorbing microwaves at the cementitious joint, the combined waste from the cementitious joint can be separated into single materials.     

Comparing the mechanical properties of cold recycled mixture containing coal waste additive and ordinary Portland cement

Pavement cold recycling is considered as an efficient rehabilitation method, especially in severely distressed roads. Modifier additives have been used for improving the performance of cold recycled mixture (CRM), especially at initial days of curing. In this study, coal waste taken from coal washing plant and its ash produced through the incineration process were used as pozzolanic additives in CRM with bitumen emulsion. To assess the effects of using these additives on mechanical properties of CRM, Marshall stability, indirect tensile strength (ITS), resilient modulus, dynamic creep and fatigue tests were applied. Furthermore, the effect of using these additives on CRM moisture sensitivity was evaluated. Application of coal waste powder improved the mechanical properties of CRM, but it could not exert a positive effect on CRM moisture sensitivity. Thus, coal waste can be used as CRM additive in conditions that moisture damage does not significantly affect the pavement performance. Unlike the coal waste powder using the coal waste ash not only increased the durability of CRM, but also it showed upgrading the mechanical properties. In continue, the mechanical properties of the CRM containing coal waste and its ash were compared with the mix that stabilised with 1% and 2% ordinary Portland cement (OPC). Based on the comparisons, coal waste powder and its ash had comparable effects to OPC. For example, the results of fatigue tests revealed that at higher strain levels of 200 μ? the fatigue life of the CRM mix containing 7% coal waste and coal waste ash was higher than that of containing 1% and 2% cement. Finally, apart from the several environmental advantages it was concluded that the use of coal waste powder and its ash had technical benefits in cold recycling with bitumen emulsion.     

Flash-calcined dredging sediment blended cements: effect on cement hydration and properties

Dredging of docks and waterways generates a large and continuous supply of sediments currently destined for disposal. Transforming this currently wasted materials into new resources still requires meeting technical challenges. One of the options is to process the sediments into a supplementary cementitious material by flash-calcination. This paper describes the effect of cement replacement by flash-calcined dredged sediments on cement hydration and key properties. The hydration kinetics, products and microstructure are studied to explain changes in cement properties such as compressive strength development and workability. The flash-calcined dredging sediments show clear pozzolanic activity which surpasses that of typical coal combustion siliceous fly ash (V, EN 197-1). This is manifested in (1) the rate of compressive strength development, (2) reduced portlandite and (3) increased ettringite and bound water contents. The results show that calcination can transform wasted dredging sediments into a new supplementary cementitious resource for producing large volumes of low-CO₂ blended cements.     

Effects of mechanical grinding on pozzolanic activity and hydration properties of quartz

To provide basic research into the utilization of mine tailings as supplementary cementitious materials in cement, the pozzolanic activity and hydration properties of quartz-a common mineral phase in mine tailings-after undergoing mechanical grinding were investigated. In this study, a supplementary cementitious material was obtained using the mechanical grinding of quartz. Prolonged grinding resulted in a gradual increase in the pozzolanic activity index and percentage of dissolution in an alkaline solution, as well as a reduction of the relative crystallinity. The particle size appeared to have reached a limit after 80 min of grinding; however, the specific surface area reached its limit after 120 min of grinding, which was mainly due to the continual increase in pore volume of the micropores and mesopores from the grinding process. As an active supplementary cementitious material, the hydration product of ground quartz was an amorphous C-S-H gel in the presence of calcium hydroxide. This study provides a research basis for investigating the pozzolanic activity and hydration properties of ground quartz, which is beneficial to an evaluation of the pozzolanic activity of siliceous mine tailings after mechanical activation.     

Determination of diffusion coefficient of chloride in concrete: an electrochemical impedance spectroscopic approach

For predicting the service life of concrete structures in marine environment, diffusion of chloride (D) is an important parameter. Electro-migration tests and ponding tests are two techniques conventionally adopted, however they are destructive in nature. EIS (Electrochemical impedance spectroscopy) being non-destructive appears a promising technique to arrive at ‘D_R’ (D from EIS) in situ in structures. The D_R of ordinary Portland cement concrete (OPC) was compared with that of Portland pozzolana cement concrete (PPC). The effect of curing on D_R was analyzed. The splash zone condition was created by subjecting the specimens to alternate wetting and drying cycles. At the end of 28 days of curing, the D_R of PPC concrete is only 66.7% of that obtained in OPC concrete. A linear correlation was established between D_R and the porosity of the concrete_. Due to pozzolanic reaction, the rate of pore refinement is faster in PPC concrete compared to OPC concrete. In M25-PPC concrete at the end of 28 days of curing, the pore size is decreased to 14.6% of that obtained at the end of 3 days of curing. The reduction of pore size by densification of pore structure due to pozzolanic reaction reduces the D_R value in PPC concrete. In 30 MPa concrete the D_R under wet cycle is 3 times higher than in dry cycle, which implied that corrosion is initiated 3 times faster in concrete exposed to the splash zone condition.     

Mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements

The benefits of limestone filler (LF) and natural pozzolana (NP) as partial replacement of Portland cement are well established. Economic and environmental advantages by reducing CO₂ emission are well known. However, both supplementary materials have certain shortfalls. LF addition to Portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, NP contributes to hydration after 28 days improving the strength at medium and later ages. Hence, ternary blended cement (OPC–LF–NP) with better performance could be produced. In this paper, mortar prisms in which Portland cement was replaced by up to 20%LF and 30%NP were tested in flexure and compressive strength at 2, 7, 28 and 90 days. Some samples were tested under sulfate and acid solutions and for chloride ions permeability. Results show that the use of ternary blended cement improves the early age and the long-term compressive and flexural strengths. Durability was also enhanced as better sulfate, acid and chloride ions penetration resistances were proved.     

Immobilization of heavy metals (Pb, Cu, Cr, Zn, Cd, Mn) in the mineral additions containing concrete composites

The presented work determines the level of heavy metals (Pb+2, Cu+2, Zn+2, Cr+6, Cd+2, Mn+2) immobilization in the composites produced using Ordinary Portland Cement (OPC) as well as of binders containing large amount of mineral additives in its composition-siliceous fly ash (FA), fluidized bed combustion ash (FFA) and ground granulated blast furnace slag (GGBFS). Heavy metals were introduced to cementitious materials in the form of soluble salts as well as components of hazardous wastes (medical ash, metallurgical dust). It has been stated, that the level of heavy metals immobilization is combined with composites composition. Majority of analyzed heavy metals, added to binders' composition in the form of heavy metal salts achieves high level of immobilization, in mortar based on binder with 85% GGBFS and 15% OPC. The lowest immobilization level was reached for chromium Cr+6 added to hardening mortars as Na2Cr2O72H2O. The level ranges from 85.97% in mortars made on blended binder (20% OPC, 30% FFA and 50% GGBFS) to 93.33% in mortar produced on OPC. The increase of the so-called immobilization degree with time of hardened material maturing was found. This should be attributed to the pozzolanic or pozzolanic/hydraulic properties of components used; their effect on microstructure of hardened material is also important. Mineral additions enter the hydration reactions in the mixtures and favor the formation of specific microstructure promoting the immobilization of hazardous elements.     

Effects of superfine zeolite on strength,flowability and cohesiveness of cementitious paste

Superfine zeolite (SFZ) is a natural zeolite ground to higher fineness than cement. Being a pozzolanic material, it can be used to replace part of the cement to reduce the cement consumption and carbon footprint of concrete production. In this study, in order to evaluate the effects of SFZ on strength and fresh properties, a total of 30 cementitious paste mixes with different SFZ contents and different W/CM ratios were produced for 7-day, 28-day, 70-day strength tests, and flowability and cohesiveness tests. And, to evaluate the effectiveness of SFZ as a superfine filler, the changes in packing density and water film thickness (WFT) due to the addition of SFZ were measured and determined. It was found that the addition of SFZ as cement replacement up to 20% slightly decreased the early strength, but slightly increased the long-term strength. Moreover, it increased the packing density and exerted its influence on the fresh properties of cementitious paste through the corresponding change in WFT. It also significantly increased the cohesiveness at the same flowability.     

Pozzolanic activity of palm bunch wastes

The paper reports an investigation of the ash from the burnt stalks of oil palm bunches as a suspected agricultural waste with pozzolanic activity. Chemical analysis confirmed the presence of the major elements silica, alumina, potassium and a comparatively low content of calcium, all of which are necessary for pozzolanic activity. Limestone, shale, lead and sodium carbonates were independently mixed with the ash to improve the pozzolanic activity, which was low without the introduction of these conditioners. It was confirmed that limestone together with lead carbonate are good additives that can enhance pozzolanic activity in the ash. The ash was therefore classified as a pozzolana which can be used to produce pozzo-lime cement or used as a blender with ordinary Portland cement.     

Influence of activated drinking-water treatment waste on binary cement-based composite behavior: Characterization and properties

Drinking water treatment plants regularly dispose of large volumes of industrial sludge in landfill sites, which often has negative environmental consequences. The calcination products of these kaolinite-based sludges have properties that could make them appropriate supplementary cementing materials in the production of blended binary cements.This research analyses the pozzolanic and thermodynamic properties of a Venezuelan drinking water sludge activated at 600 °C for 2 h and its behavior in blended cement matrices prepared with 15% Activated Waste (AW) and 85% Ordinary Portland Cement (OPC). Our results show that this activated drinking water sludge presents high pozzolanic properties, mainly during the first 24 h of reaction. The XRD, SEM/EDX and thermodynamic studies confirm the formation of C₂ASH₈, C–S–H gels and C₄AH₁₃ as the hydration products from the pozzolanic reaction. The binary mixture of 15% AW/85% OPC complied with the physical and mechanical specifications contained in current European cement standards.     

The effect of high salt concentration on the integrity of silica-fume blended cementitious matrices for waste immobilization applications

Silica Fume is a commonly used pozzolanic additive for cementitious matrices used for immobilization of Low Level Waste (LLW). Cementitious systems containing silica-fume are used to reduce the leachability of various hazardous species. However, during the last years several publications have shown that commercially available densified silica-fume (DSF) does not fully disperse within cementitious pastes and concrete mixes, but rather tends to form agglomerated particles which range in size from tens to hundreds of microns. Cementitious matrices containing such agglomerates are prone to the alkali-silica reaction (ASR). As radioactive waste streams often contain high alkali salt concentrations, the occurrence of ASR, deleterious osmotic pressure or other degradation mechanisms in cementitious waste matrices must be considered. The aim of this research was to study the effect of high salt content in DSF bearing pastes on the integrity of the immobilized waste form and its efficiency to immobilize low level radioactive waste. The dependence of matrix integrity on both salt and silica fume concentration is presented.     

Use of calcium carbide residue and bagasse ash mixtures as a new cementitious material in concrete

Calcium carbide residue (CCR) is a by-product of the acetylene gas production and bagasse ash (BA) is a by-product obtained from the burning of bagasse for electricity generation in the sugar industry. The mixture between CCR contains a high proportion of calcium hydroxide, while BA is a pozzolanic material, can produce a pozzolanic reaction, resulting in the products similar to those obtained from the cement hydration process. Thus, it is possible to use a mixture of CCR and BA as a cementitious material to substitute for Portland cement in concrete. The results indicated that concrete made with CCR and BA mixtures and containing 90 kg/m³ of Portland cement gave the compressive strength of 32.7 MPa at 28 days. These results suggested that the use of ground CCR and ground BA mixtures as a binder could reduce Portland cement consumption by up to 70% compared to conventional concrete that requires 300 kg/m³ of Portland cement to achieve the same compressive strength. In addition, the mechanical properties of the alternative concrete including compressive strength, splitting tensile strength, and elastic modulus were similar to that of conventional concrete.