Analysis of alternative water sources for use in the manufacture of concrete

In Australia and many other countries worldwide, water used in the manufacture of concrete must be potable. At present, it is currently thought that concrete properties are highly influenced by the water type used and its proportion in the concrete mix, but actually there is little knowledge of the effects of different, alternative water sources used in concrete mix design. Therefore, the identification of the level and nature of contamination in available water sources and their subsequent influence on concrete properties is becoming increasingly important. Of most interest, is the recycled washout water currently used by batch plants as mixing water for concrete. Recycled washout water is the water used onsite for a variety of purposes, including washing of truck agitator bowls, wetting down of aggregate and run off. This report presents current information on the quality of concrete mixing water in terms of mandatory limits and guidelines on impurities as well as investigating the impact of recycled washout water on concrete performance. It also explores new sources of recycled water in terms of their quality and suitability for use in concrete production. The complete recycling of washout water has been considered for use in concrete mixing plants because of the great benefit in terms of reducing the cost of waste disposal cost and environmental conservation. The objective of this study was to investigate the effects of using washout water on the properties of fresh and hardened concrete. This was carried out by utilizing a 10 week sampling program from three representative sites across South East Queensland. The sample sites chosen represented a cross-section of plant recycling methods, from most effective to least effective. The washout water samples collected from each site were then analysed in accordance with Standards Association of Australia AS/NZS 5667.1 :1998. These tests revealed that, compared with tap water, the washout water was higher in alkalinity, pH, and total dissolved solids content. However, washout water with a total dissolved solids content of less than 6% could be used in the production of concrete with acceptable strength and durability. These results were then interpreted using chemometric techniques of Principal Component Analysis, SIMCA and the Multi-Criteria Decision Making methods PROMETHEE and GAIA were used to rank the samples from cleanest to unclean. It was found that even the simplest purifying processes provided water suitable for the manufacture of concrete form wash out water. These results were compared to a series of alternative water sources. The water sources included treated effluent, sea water and dam water and were subject to the same testing parameters as the reference set. Analysis of these results also found that despite having higher levels of both organic and inorganic properties, the waters complied with the parameter thresholds given in the American Standard Test Method (ASTM) C913-08. All of the alternative sources were found to be suitable sources of water for the manufacture of plain concrete.

Effects of unconfined concrete strength on FRP confinement of concrete

Research has shown that fibre reinforced polymer (FRP) wraps are effective for strengthening concrete columns for increased axial and flexural load and deformation capacity, and this technique is now used around the world. The experimental study presented in this paper is focused on the mechanics of FRP confined concrete, with a particular emphasis on the influence of the unconfined concrete compressive strength on confinement effectiveness and hoop strain efficiency. An experimental programme was undertaken to study the compressive strength and stress-strain behaviour of unconfined and FRP confined concrete cylinders of different concrete strength but otherwise similar mix designs, aggregates, and constituents. This was accomplished by varying only the water-to-cement ratio during concrete mixing operations. Through the use of high-resolution digital image correlation to measure both axial and hoop strains, the observations yield insights into the mechanics of FRP confinement of concretes of similar composition but with varying unconfined concrete compressive strength.

The influence of the mixing time in the rheological behavior of cement pastes

Rheology has the purpose to study the flux and deformation of materials when submitted to some tension or outer mechanical solicitation. In practice, the effective scientific field broached by rheology is restricted only to the study of homogeneous fluids behavior, in which are included eminent liquids, particles suspensions, and emulsions. The viscosity (η) and the yield stress (τ 0) are the two basic values that define the fluids' behavior. The first one is the proportionality constant that relates the shear rate (γ) with the shear stress (τ) applied, while the second indicates the minimal tension for the flowage beginning. The fluids that obey the Newton's relation - Newtonians fluids - display the constant viscosity and the null yield stress. It's the case of diluted suspensions and grate amount of the pure liquids (water, acetone, alcohol, etc.) in which the viscosity is an intrinsic characteristic that depends on temperature and, in a less significant way, pressure. The suspension, titled Cement Paste, is defined as being a mixture of water and cement with, or without, a superplasticizer additive. The cement paste has a non-Newtonian fluid behavior (pseudoplastic), showing a viscosity that varies in accord to the applied shear stress and significant deformations are obtained from a delimited yield stress. In some cases, systems can also manifest the influence of chemical additives used to modify the interactions fluid/particles, besides the introduced modifications by the presence of incorporated air. To the cement paste the rheometric rehearsals were made using the rheometer R/S Brookfield that controls shear stress and shear rate in accord to the rheological model of Herschel-Bulkley that seems to better adapt to this kind of suspension's behavior. This paper shows the results of rheometrical rehearsals on the cement paste that were produced with cements HOLCIM MC-20 RS and CPV-ARI RS with the addition of superplasticizer additives based of napthaline and polycarboxilate, with and without a constant agitation of the mixture. The obtainment of dosages of superplasticizer additives, as well as the water/cement ratio, at the cement at the fluidify rate determination, was done in a total of 12 different mixtures. It's observed that the rheological parameters seem to vary according to the cement type, the superplasticizer type, and the methodology applied at the fluidity rate determination.

Desenvolvimento e avaliação de um sistema de monitorização da corrosão electroquímica no betão armado

O presente trabalho teve como principal objectivo desenvolver e avaliar o desempenho de um sistema de monitorização da corrosão no betão armado. Para tal foram construídos dois provetes de classe 20/25, e outros dois de classe 30/35. Dentro desses quatro provetes foram instalados sensores de corrosão designados por Monicorr. Para cada classe de betão utilizaram-se dois tipos diferentes de contaminação, designadas por A e B. A contaminação do tipo A é feita adicionando durante a amassadura do betão uma solução aquosa de cloreto de cálcio a 4% em massa de cimento e sujeitando esses provetes a ciclos de condensação de 50h, durante um período de 1000h. A contaminação do tipo B é feita sujeitando os outros dois provetes de classes diferentes a ciclos de 100h de nevoeiro salino a 3% em massa de água, durante um período de 2000h. Para avaliar o desempenho do sistema de monitorização Monicorr foram comparados os valores da velocidade de corrosão instantânea por LPR, a resistividade do betão e o potencial de corrosão da armadura, obtidos pelo sistema Monicorr, com os obtidos por aparelhos utilizados para o mesmo efeito em laboratório. Paralelamente, estudou-se também a variação do potencial de corrosão da armadura em função da área oxidada. Para além disso desenvolveu-se um conjunto de pseudo referências de grafite dopada com diferentes percentagens de cimento e avaliou-se a sua estabilidade relativamente ao eléctrodo de calomelanos e óxido de managanês manganês em soluções de hidróxido de cálcio saturada e de betão armado contaminado com sais cloreto. Finalmente foram ainda desenvolvidas duas tarefas, a primeira relacionada com os resultados obtidos na medição da resistividade do betão armado pelas técnicas de dois pinos e quatro pinos, e a segunda com o desenvolvimento de um método rápido de contaminação do betão armado com dióxido de enxofre. Os resultados obtidos permitem concluir que: - o sistema de monitorização Monicorr apresenta um comportamento muito semelhante aos utilizados em laboratório para medir grandezas como o potencial de corrosão da armadura, resistividade do betão e velocidade de corrosão instantânea por LPR; - a monitorização das três grandezas atrás referidas pode ser uma ferramenta importante para permitir saber qual é o desenvolvimento corrosivo de uma estrutura de betão armado; os eléctrodos de grafite dopada com cimento apresentam uma elevada estabilidade nos meios testados tendo um desempenho muito semelhante à referência de manganês óxido de manganês para os mesmos meios. Relativamente à influência da área oxidada no potencial de corrosão da armadura não foi possível tirar conclusões. Foi possível, também, concluir que existe uma clara concordância entre as medições da resistividade do betão utilizando o método dos dois pinos e o método dos quatro pinos. Finalmente pode-se concluir que a metodologia desenvolvida para contaminar provetes de betão com iões sulfato obtém bons resultados ao fim de, apenas, 48h de contaminação.

Radford's cyclopedia of cement construction; a general reference work on up-to-date practice in the manufacture and testing of cements; the selection of concreting materials, tools, and machinery; the proportioning, mixing, and depositing of concrete, and its application to all types and reinforced; together with analysis of the principles of constructive design, cost estimating, and the allied branches of stone and brick masonry and steel construction; based on the practical experience of a large staff of experts in actual construction work ...

"Prepared under the supervision of William A. Radford, editor-in-chief ... Alfred Sidney Johnson ... editor in charge."

Casting of Self-Compacting Concrete

Increased productivity and improved working environment have had high priority in the development of concrete construction over the last decade. Development of a material not needing vibration for compaction—i.e. selfcompacting concrete (SCC)—has successfully met the challenge and is now increasingly being used in routine practice. The key to the improvement of fresh concrete performance has been nanoscale tailoring of molecules for surface active admixtures, as well as improved understanding of particle packing and of the role of mineral surfaces in cementitious matrixes. Fundamental studies of rheological behaviour of cementitious particle suspensions were soon expanded to extensive innovation programmes incorporating applied research, site experiments, instrumented full scale applications supporting technology, standards and guides, information efforts as well as training programmes. The major impact of the introduction of SCC is connected to the production process. The choice and handling of constituents are modified as well as mix design, batching, mixing and transporting. The productivity is drastically improved through elimination of vibration compaction and process reorganisation. The working environment is significantly enhanced through avoidance of vibration induced damages, reduced noise and improved safety. Additionally, the technology is improving performance in terms of hardened material properties like surface quality, strength and durability.

Sustainable binders for concrete: a structured approach from waste screening to binder composition development

Worldwide, the building sector requires the production of 4 billion tonnes of cement annually, consuming more than 40% of global energy. Alkali activated “cementless” binders have recently emerged as a novel eco-friendly construction material with a promising potential to replace ordinary Portland cement. These binders consist of a class of inorganic polymer formed mainly by the reaction between an alkaline solution and an aluminosilicate source. Precursor materials for this reaction can be found in secondary material streams from different industrial sectors, from energy to agro-alimentary. However, the suitability of these materials in developing the polymerisation reaction must be assessed through a detailed chemical and physical characterisation, ensuring the availability of required chemical species in the appropriate quantity and physical state. Furthermore, the binder composition needs to be defined in terms of proper alkali activation dosages, water content in the mix, and curing conditions. The mix design must satisfy mechanical requirements and compliance to desired engineering properties (workability, setting time) for ensuring the suitability of the binder in replacing Portland cement in concrete applications. This paper offers a structured approach for the development of secondary material-based binders, from their identification to mix design and production procedure development. Essential features of precursor material can be determined through chemical and physical characterisation methods and advanced microscope techniques. Important mixing parameters and binder properties requirements are examined and some examples of developed binders are reported.

Compressive and flexural properties of hemp fiber reinforced concrete

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.

Properties of hemp fibre reinforced concrete composites

This research is concerned with the mechanical and physical properties of hemp fibre reinforced concrete (HFRC). An experimental program was developed based on the statistical method of fractional factors design. The variables for the experimental study were: (1) mixing method; (2) fibre content by weight; (3) aggregate size; and (4) fibre length. Their effects on the compressive and flexural performance of HFRC composites were investigated. The specific gravity and water absorption ratio of HFRC were also studied. The results indicate that the compressive and flexural properties can be modelled using a simple empirical linear expression based on statistical analysis and regression, and that hemp fibre content (by weight) is the critical factor affecting the compressive and flexural properties of HFRC.

Study of the Influence of Fines on a Self-Compacting Concrete

The paper presents the results of the tests of a self-compacting concrete made with fines which include Portland cement and three fillers: hornfels, limestone and metakaolin, in a weight proportion between 23% and 45% of the admixtures. The first mix proportions were designed with a high proportion of Portland cement (720-750kg/m3), and are compared to those having a smaller content of cement and more fillers. The results obtained show that the limestone filler percentage should be higher than the hornfels one, and both of them significantly higher than that of the metakaolin so as to facilitate the fluidity and self-compactability. AIso, the higher proportion of fillers causes a rounded porosity in the mixing which has a bearing on better compressive strength results.

Organizational maintenance repair parts and special tools lists : dryer, aggregate, diesel engine driven, 4 wheel mtd. NSN 3895-00-236-8123 : Barber-Greene MDL DA-60 : components of mixing plant asphalt, 100-150 ton per hour NSN 3895-00-936-8613.

Includes index.

Direct support and general support maintenance repair parts and special tools lists : dryer, aggregate, diesel engine driven, 4 wheel mtd., NSN 3895-00-236-8123, Barber-Greene MDL DA-60 : component of mixing plant asphalt, 100-150 ton per hour, NSN 3895-00-936-8613, Barber-Greene MDL KA-60.

Includes indexes.

Organizational maintenance repair parts and special tools lists : mixer, bituminous material, non-self loading, DED, NSN 3895-00-933-0577, Barber-Greene model KA60, component of mixing plant, asphalt, 100-150 ton per hour, NSN 3895-00-936-8613.

Includes index.

Direct support and general support maintenance repair parts and special tools lists (including depot maintenance repair parts and special tools lists) : mixer, bituminous material, non-self loading, DED, NSN 3895-00-933-0577, Barber-Greene model KA60, component of mixing plant, asphalt 100-150 ton per hour, NSN 3895-00-936-8613.

Includes index.

Unit, direct support, and general support maintenance repair parts and special tools lists : drier-mixer, bituminous, concrete material, wheel mounted, GED, 2-wheel, pneumatic tires, 3 to 10 tons per hour (NSN 3895-00-832-6230).

"June 1992."