Halogen ligth thermogravimetric technique for determining the retained water in fine aggregates used for concrete mixing design

[EN] Measuring the rate of water retention of the aggregates used in mortars and concrete is required to achieve a good mix design. The water retention, specifically absorption, is used to keep constant the water/cement ratio. This paper focuses on the study of a new technique for measuring retained water in fine aggregates. In order to obtain results, the procedure described in the existing standards takes more than 24 h. Additionally, it involves high consumption of heat energy due to the use of drying ovens. Furthermore, the results obtained remain highly variable and therefore discussed by the scientific community.In this research, a novel technique based on a halogen moisture analyzer was implemented. The technique was assessed using an experiment design with a surface response model. The most important factors and levels were identified together with the interactions between them. Finally, the model was validated and the results obtained with this technique were compared with those obtained by conventional techniques in order to verify that they were equivalent.Arias Jaramillo, Y.; Paya Bernabeu, JJ.; Ochoa Botero, JC. (2015). Halogen ligth thermogravimetric technique for determining the retained water in fine aggregates used for concrete mixing design. Journal of Thermal Analysis and Calorimetry: an international forum for thermal studies. 123:127-134. doi:10.1007/s10973-015-4902-8S127134123Djerbi Tegguer A. Determining the water absorption of recycled aggregates utilizing hydrostatic weighing approach. Constr Build Mater. 2012;27:112–6.Kasemchaisiri R, Tangtermsirikul S. A method to determine water retainability of porous fine aggregate for design and quality control of fresh concrete. Constr Build Mater. 2007;21:1322–34.Gonilho Pereira C, Castro-Gomes J, Pereira de Oliveira L. Influence of natural coarse aggregate size, mineralogy and water content on the permeability of structural concrete. Constr Build Mater. 2009;23:602–8.Cortas R, Roiziére E, Staquet S, Hamami A, Delplancke-Ogletree M. Effect of the water saturation of aggregates on the shrinkage induced cracking risk of concrete at early age. Cem Concr Compos. 2014;50:1–9.Black R. The determination of specific gravity using Siphon-Can method. Cem Concr Aggreg. 1986;8:46–50.Saxer E. A direct method of determining absorption and specific gravity of aggregates. 1956;2.Hughes B, Famili H., Part 1—Absorption of concrete aggregates, Part 2—saturated air techniques for determining the absorption of aggregates. In: Absorptions of concrete aggregates. Birmingham University; 1971.Tam VWY, Gao XF, Tam CM, Chan CH. New approach in measuring water absorption of recycled aggregates. Constr Build Mater. 2008;22:364–9.Balcedowiak W. Phase analysis of high-calcium line by TG. J Therm Anal Calorim. 2000;60:70–7.Mendoza O, Tobón JI. An alternative thermal method for identification of pozzolanic activity in Ca(OH)2/pozzolan pastes. J Therm Anal Calorim. 2013;114:589–96.Kosmatka SH, Kerkhoff B, Panarese W, MacLeod NF, McGrath RJ, Design and control of concrete mixtures. 7rd ed. Cement association of Canada. 2002. pp. 88.Cárdenas JI, Restrepo C. Patrimonio geológico y patrimonio minero de la cuenca carbonífera del suroeste antioqueño, Colombia. Boletín de ciencias de la tierra. 2006;18:91–102 ISSN 0120-3630 .Klein NS, Aguado A, Tollares-Carbonari BM, Real LV. Prediction of the water absorption by aggregates over time: modelling through the use of value function and experimental validation. Constr Build Mater. 2014;69:213–20

Determining the water absorption of recycled aggregates utilizing hydrostatic weighing approach

The water absorption of aggregates is a key parameter in concrete mix design. As the adhered mortar of recycled aggregates present a long time of saturation (>24 h). A new approach of water absorption measurement was developed using hydrostatic weighing in order to observe the kinetic absorption of aggregates, and to obtain a necessary water quantity added in different steps in concrete mix. Experimentalresults indicate that the model of capillarity processes of aggregates can be obtained using Hall's model. A good correlation was obtained between the current method NF EN 1097-6 and hydrostatic weighing approach. A necessary time for the total saturation of recycled aggregates was evaluated

Influence of the saturation state of recycled sand on mortars compressive strength

This paper investigates the water content of pre-saturated recycled concrete aggregates (RCA) that has a diameter of 1-4 mm called recycled sand (RS), in order to determine the degree of saturation of the RS. It also puts forward the effects of the saturation state of the RS on the mechanical properties. For this matter, experiments were conducted in this research as: evaporation method to determine the water content of the RS and the compressive strength of mortars. These properties are tested for different saturation states and different saturation methods of the RS and for two types of curing conditions: laboratory curing conditions (LCC) and water immersion conditions (WIC). Results show that the standard method (NF EN 1097-6) largely underestimates the water absorption coefficient of RCA and that the saturation state of the RS and curing conditions affects the compressive strength of mortar

Effect of uniaxial compressive loading on gas permeability and chloride diffusion coefficient of concrete and their relationship

International audience10 Knowledge of the transport properties of damaged concrete in marine environments is 11 essential for predicting its durability. The objective of this study was to fill this gap by 12 correlating the change in permeability and chloride diffusivity with an increasing uniaxial 13 load on ordinary concrete (OC) and high performance concrete (HPC). Concrete cylinders 14 were induced microcracks by mechanical uniaxial compression between 60% and 90% of the 15 ultimate strength to get diffuse damage. The damage variable of specimens was evaluated by 16 elastic stiffness degradation and ultrasound pulse velocity. After unloading intrinsic gas 17 permeability was measured using a constant head permeameter, the chloride migration 18 coefficient was evaluated by migration test in steady state conditions, with the same concrete 19 specimen. The damage variable of specimens showed correlation with gas permeability and 20 chloride diffusion of concrete in this experiment. A linear correlation was obtained between 21 intrinsic permeability coefficient and chloride diffusion coefficient depending on the damage 22 variable, specific for each concrete type (OC and HPC). 23 24 2

Some Properties of concretes containing recycled aggregates

International Conference on Sustainable Structural Concrete, LA PLATA, ARGENTINE, 15-/09/2015 - 18/09/2015This paper presents the results of an experimental campaign which aimed at determining the viability of incorporating recycled aggregates from concrete, in the production of a new concrete, with acceptable performances for its use in new structures. Nine concrete mixtures with different recycled aggregates contents and with different water to binder (w/b) ratio were studied. The mean compressive strength for the reference concretes is comprised between 30 and 60 MPa. Tests were performed to measure compressive strength, porosity, chloride diffusion and gas permeability. The results indicated that the porosity of recycled aggregates concrete strongly depends on recycled aggregates contents. Chloride diffusion and permeability are also modified. For practical use, it is important to note that these durability properties can be improved by the optimization of the mix, in particularly the w/b ratio of the new concrete

Propriétés des bétons de granulats recyclés

GC'2015, Paris, FRANCE, 18-/03/2015 - 19/03/2015L'utilisation de granulats recyclés (GR) provenant de la déconstruction dans de nouvelles structures en béton peut permettre de valoriser ces déchets. En France, le projet national RECYBETON impliquant 43 partenaires pour un budget de 4,8 M d'euros et le projet ANR ECOREB s'intéressent à lever les verrous technologiques concernant ce type de granulat afin de mieux maitriser leur utilisation et de les introduire encore d'avantage dans le contexte normatif. Plusieurs travaux ont été réalisés pour étudier l'utilisation des GR en remplacement partiel ou total des granulats naturels (GN) dans la fabrication de nouveaux bétons [1,2]. La faible densité et le taux d'absorption d'eau élevé des GR sont les facteurs influençant le plus les propriétés des bétons de GR. De nombreux auteurs attribuent ces différences aux propriétés du mortier d'origine contenu dans les granulats recyclés [3,4]. D'autres études montrent que le béton à base de GR grossiers découlant du recyclage peut avoir des propriétés mécaniques similaires à celles des bétons classiques [5]. Cet article propose une nouvelle approche permettant d'améliorer les propriétés des bétons de GR (la résistance à la compression, la porosité, la diffusion des chlorures et la perméabilité au gaz), en optimisant la formulation des bétons (le rapport E/L et la quantité de superplastifiant)

Durabilité des structures en béton incorporant des granulats recyclés

Conférence Internationale Francophone NoMaD, Nouveaux Matériaux et Durabilité, Douai, FRANCE, 05-/11/2015 - 06/11/2015De nos jours, le développement durable occupe une place de plus en plus importante dans la société. Deuxième matériau le plus consommé dans le monde après l'eau, le béton fait l'objet de nombreuses études destinées à valoriser sa réutilisation lors de la fin de vie des constructions. En ce sens, le projet national français RECYBETON et le projet ANR ECOREB associé visent à lever les verrous techniques concernant la réutilisation de béton issu de la déconstruction sous forme de granulat. Un des objectifs du projet ANR ECOREB consiste à évaluer l'influence des granulats issus du recyclage sur les propriétés de durabilité des bétons liées aux risques de corrosion des armatures. Les précédents travaux réalisés sur le sujet ont mis en évidence que les granulats issus de béton concassé sont généralement plus poreux que les granulats traditionnels et conduisent à une diminution des propriétés de durabilité. Les travaux présentés dans cet article portent sur la résistance des bétons incorporant des granulats recyclés à la carbonatation et à la migration des chlorures. Des analyses comparatives ont été menées sur trois familles de bétons de différentes classes de résistance : C25/30, C35/45 et C45/55. Pour chacune des familles, trois bétons ont été réalisés : deux avec des granulats recyclés, un troisième comportant des granulats traditionnels (référence). Pour chaque famille de béton, deux types de cure ont été étudiés : une cure humide (conservation 90 jours dans l'eau) et une cure "sèche" (conservation 3 jours dans l'eau puis 87 jours à 20 °C et 60 % d'humidité relative). Des essais accélérés de carbonatation et de migration des ions chlorure sous champs électrique en régime transitoire ont été réalisés sur ces bétons

Improvement of Recycled Aggregates Properties by Means of CO2 Uptake

Concrete from deconstruction can have a second life in the form of recycled concrete aggregates (RCAs). They unfortunately have poor properties (high porosity and water absorption coefficient (WAC)) with respect to natural aggregates. Accelerated carbonation was implemented to improve the RCA properties and to increase their use by storing carbon dioxide (CO2 ) in the cement matrix and thereby reduce their environmental impact. This paper aims to perform a parametric study of a process for accelerated carbonation of RCAs to store the largest possible amount of CO2 and improve their properties. This study highlights the fact that each of these parameters affects CO2 storage, with an optimum water content for the maximum CO2 uptake depending on the nature and the source of the RCAs. This optimum is related to the RCA water absorption coefficient by a linear relationship. The results show that accelerated carbonation reduces the water absorption coefficient by as much as 67%. Finally, carbonation also decreases porosity, as observed by mercury intrusion porosimetry, by filling the capillary pores