New model for natural carbonation prediction in reinforced concrete – concept and validation on chemical admixtures

Abstract: A new model for prediction of natural carbonation in reinforced concrete structures has recently been developed and presented in (Ekolu, 2018). For brevity, the model is referred to as ESS model. It employs concrete strength as the primary property depicting core carbonation behaviour of any given concrete while other factors induce secondary influence. Chemical admixtures in concrete significantly influence concrete behaviour. Using experimental data from the literature (Dan-Herrera et al., 2015), the model behaviour is verified under use of various types of chemical admixtures of concrete including internal curing, shrinkage reducing, viscosity modifying, and high range water reducing admixtures. Class F fly ash was also used in the concrete mixtures as a supplementary cementitious material. Verification results show the model predictions to be meaningful and consistent with robustness

Modification in clay concrete properties during fluid flow permeability measurement

Abstract: In this paper, two methods consisting of triaxial water permeability and water penetration were used to evaluate changes occurring in the pores of clay concretes, during the tests. Triaxial permeability is generally used for concrete with higher permeability while concrete with very low permeability are suited for the penetration method. Clay concrete specimens of 0 to 40% clay content were used in the study. The concrete mixes had water-to-cementitious ratios (w/cc) of 0.70, 0.75, 0.80, 0.85, and the cementitious content 380 and 450 Kg/m3. Results show that concrete gains moisture during wetting at a much faster rate than it loses during subsequent drying. This could be explained by the contribution of suction pressure created upon drying. When water penetration pressure is applied, more water is driven into pore space than could be responsible for changing the network of the voids. Pore structure during drying may certainly be different in size and shape than its form during wetting, leading to a consequent effect on the permeability of the clay concretes. The modification could be one reason that the moisture gain percentage in clay concretes was higher than in normal concretes

Effect of mix parameters on strength of geopolymer mortars - experimental study

Abstract: In this article, an investigation is reported on development of strength in South African fly ash (FA) – based geopolymer mixtures. Locally available Class F, FA from one of the coal power stations was used in the investigation. The alkali-activator used consisted of sodium silicate (SS) and sodium hydroxide (SH) mixed in varied ratios of 1.0, 1.5, 2.0, 2.5 and 3.0 SS to SH. The SS of silicate modulus = 2.5 was used but the SH concentration in the activator was varied to 10, 12, 14M NaOH. Mortars of 2.25 aggregate/binder ratio were used to prepare 50 mm cubes. In preparing mortar mixtures, the liquid to solids (L/S) ratios were varied to L/S = 0.3, 0.4, 0.5 and 0.6. Mortar cubes were cast and cured at 80oC for 7 days then tested for compressive strength. It was found that all three parameters consisting of SS/SH ratio of the activator, concentration of NaOH used in the activator and the L/S ratio, showed significant influence upon compressive strength development. The optimum strength of the geopolymer mortar mixtures was obtained at SS/SH = 2.0, 12M NaOH concentration ad L/S = 0.5

Enhancing the reactivity of aluminosilicate materials towards geopolymer synthesis

Abstract: Geopolymers are alternative materials to portland cement, obtained by alkaline activation of aluminosilicates. They exhibit excellent properties and a wide range of potential applications in the field of civil engineering. Several natural aluminosilicates and industrial by-products can be used for geopolymer synthesis, but a lot of starting materials have the disadvantage of poor reactivity and low strength development. This paper presents a comprehensive review of the main methods used to alter the reactivity of aluminosilicate materials for geopolymer synthesis, as reported recently in the literature. The methods consist of mechanical, thermal, physical separation and chemical activation, of which mechanical activation is the most commonly employed technique. The reactivity of the activated aluminosilicate materials is mainly related to the activation method and the treatment parameters. Chemical activation by alkaline fusion is a promising method allowing preparation of one-part geopolymer materials, an alternative class of geopolymeric binders. However, the resulting alkaline-fused geopolymer products are vulnerable to attack by excessive alkalis

Quality of water recovered by treating acid mine drainage using pervious concrete adsorbent

Abstract : In this paper, a batch experiment was conducted to evaluate the water quality obtained from using pervious concrete (PERVC) technology to treat acid mine drainage (AMD). The study proposes an innovative application of PERVC as a permeable reactive barrier liner in evaporation ponds. The effectiveness of PERVC adsorbent in removing heavy metals was compared with that of zero-valent iron (ZVI) of particles sizes 1.0 to 1.8 mm. The AMD used in the study was obtained from abandoned gold and coal mines. PERVC mixtures consisted of granite aggregate and ordinary portland cement CEM I 52.5R (CEM I) or CEM I containing Class F 30% fly ash (30%FA) as a cement replacement material. ZVI was prepared from a mixture of silica sand and iron grit of specific sizes. PERVC and ZVI media were used to conduct batch reactor tests with AMD, for a period of 43 days at a ratio of one litre of reactive material to three litres of AMD. The quality of treated AMD was compared against effluent discharge standards. The contaminants Al, Fe and Zn were effectively removed by both PERVC and ZVI. Also, both adsorbents reduced Ni, Co and Cu to levels below those measured in raw AMD. However, PERVC was more effective in removing Mn and Mg while ZVI was ineffective. Although PERVC removed more heavy metals and with greater efficiency than ZVI, the PERVC – treated water showed high pH levels and exhibited elevated Cr6+ concentrations, owing to leaching from the cement and fly ash materials used in PERVC mixtures

Evaluation and microanalytical study of ZVI /zeolite substrate mixtures for treating acid mine drainage using reactive barriers - removal mechanisms

Abstract: Batch and column experiments were performed to evaluate contaminant removal from acid mine drainage (AMD) using volcanic ash zeolite (VA) with or without zero-valent iron (ZVI) media. Two types of AMD were used i.e. WZ with pH of 2.43 taken from goldfields and TDB with pH of 2.93 collected from coalfields. It was found that VA substrate performed similarly or better than ZVI reactive media whose pH reached 7.0 to 8.5. VA was effective in removing heavy metals despite attaining a relatively lower maximum pH of 5.5. Metals Al, Fe, Zn were generally completely removed from both types of AMD by both the VA and ZVI substrates and their 50:50 mixtures. Removal of Mg and Mn was influenced by the type of AMD. Generally, the substrate comprising 50:50 ZVI/VA mixture was found to treat both AMD types fairly consistently, achieving complete removal of major elements in TDB and a majority of other elements in WZ..

Statistical analysis of concrete cover in new highway bridges

Abstract: Quality control is one of the important aspects of any major construction works, that is to be undertaken to ensure work execution according to design requirements. The work presented in this paper involved measurement of cover thickness in three newly constructed highway bridges. Testing was conducted to ensure that specified requirements were attained prior to commissioning of the structures; otherwise, the quality control survey would identify problem areas for consideration of corrective measures. A total of 328 data sets were obtained during cover measurements. In this paper, the results obtained are discussed and evaluated. Data are characterised on the basis of statistical quantitie

Pozzolanic materials and waste products for formulation of geopolymer cements in developing countries : a review

Abstract: Potential use of Geopolymers as binders in concrete instead of ordinary Portland cement (OPC) has attracted worldwide attention in recent years, due to its advantages such as environmental benefits, better durability and acceptable mechanical properties. In this paper, it is shown that the large resources of aluminosilicate waste materials in developing countries present a great opportunity for their use to make geopolymer concretes towards building of local physical infrastructure. This paper reviewed research on characteristics and properties of geopolymer binders and concretes. The effects of different raw materials, various activators, mixture formation and curing are discussed

Effects of using glasswaste cullets as aggregates in concrete

Abstract: Glass recycling in South Africa is actively employed to promote environment sustainability. However, considerable quantities of waste are generated during this recycling process, which is disposed-off to landfills. The present study was conducted to investigate potential use of glass waste cullets in concrete. Concrete of water/cement ratio = 0.75 was used to prepare 100 mm (4 in.) cubes, 100 x 100 x 200 mm (4 x 4 x 8 in.) double cubes and 50 x 50 x 285 mm (2 x 2 x 11.4 in.) prisms. Control mixtures were made using crushed granite coarse and fine aggregates, then glasswaste cullets were incorporated as sand replacements in proportions of 0, 30, 50 and 70% glass..

A comprehensive mix design method for fly ash Geopolymer Mortars

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