The Influence of Wastes Materials on the Rheology of Rendering Mortars
Total Page：16
File Type：pdf, Size：1020Kb
The Influence of Wastes Materials on the Rheology of Rendering Mortars L. A. Pereira de Oliveira, J.P. Castro Gomes and M.C.S. Nepomuceno C-MADE, Centre of Materials and Building Technologies, University of Beira Interior, Calçada Fonte do Lameiro, 6201-001 Covilhã, Portugal * Corresponding author: [email protected] Received: 26.12.2011, Final version: 20.9.2012 Abstract: The objective of this paper is to present the results of a research about the effect of mineral additions and spe- cific lightweight aggregates obtained from wastes materials (crushed EPS and cork) on the rheological proper- ties of renderings mortars. Four series of mortar formulations were prepared. Each series was composed by four mortars mixes with different mineral additions: hydrated lime, glass powder, tungsten mine waste mud, and metakaolin. The proportions of the mortars expressed in terms of apparent volume of cement, mineral addition and sand was 1:1:5. Flowability of mortar was measured using a standard flow table test. The density and the water retention capacity of mortars were also determined. The mortar rheological parameters were evaluated using a rheometer. The results show that the mortar yield stress is strongly influenced by the water amount, binder fineness and mineral addition nature. The mortars plastic viscosity is also influenced by the nature of mineral addition and the partial replacement of sand by EPS aggregates introduce incongruent values, caused by the segregation, in the mortar yield stress, whereas, the cork aggregates is responsible by the yield stress reduction. Zusammenfassung: Die Zielsetzung dieses Artikels ist, Forschungsresultate zu präsentieren über den Einfluss mineralischer Zusatz- stoffe und spezieller Aggregate mit niedriger Dichte aus Abfallmaterialien (zerkleinertes EPS und Kork) auf die rheologischen Eigenschaften von Putzmörtel. Vier verschiedene Mörtelformulierungen wurden untersucht. Jede Formulierung bestand aus vier Mörtelmischungen mit unterschiedlichen mineralischen Additiven: hydratisier- ter Kalk, Glaspulver, Wolframminenabbaulehm und Metakaolinit. Die Zusammensetzung (scheinbare Volu- menanteile von Zement, mineralischen Additiven und Sand) des Mörtels war 1:1:5. Die Fließfähigkeit des Mör- tels mit Hilfe des Standardfließtischtests wurde gemessen. Die Dichte und das Rückhaltevermögen bzgl. Wasser wurden ebenfalls bestimmt. Die rheologischen Eigenschaften des Mörtels wurden mit Hilfe eines Rheometers bestimmt. Die Ergebnisse zeigen, dass die Fließspannung des Mörtels stark durch den Wasseranteil, die Fein- heit des Binders und die Natur der mineralischen Additive beeinflusst wird. Die plastische Viskosität des Mör- tels wird auch durch die Natur der mineralischen Zusatzstoffe beeinflusst, und der partielle Ersatz des Sandes durch EPS-Aggregate führt nichtübereinstimmende Werte ein, verursacht durch Segregation in der Fließspan- nung des Mörtels, wohingegen die Korkaggregate für die Reduktion der Fließspannung verantwortlich sind. Résumé: L'objectif de cet article est de présenter les résultats d'une recherche sur l'effet des additions minérales et des granulats légers obtenus à partir de matières de déchets (Polystyrène expansé EPS et le liège) sur les propriétés rhéologiques des mortiers. Quatre séries de formulations de mortier ont été préparées. Chaque série a été com- posée de quatre mélanges avec différentes additions minérales: chaux hydratée, poudre de verre, boue de déchets de mine de tungstène et metakaolin. Les proportions des mortiers exprimées en termes de volume appa- rent du ciment, du sable et d’addition minéral est 01:01:05. L’ouvrabilité du mortier a été mesurée en utilisant la table à secousses. La masse volumique apparente et la capacité de rétention d'eau des mortiers ont égale- ment été déterminées. Les paramètres rhéologiques du mortier ont été évalués à l'aide d'un rhéomètre. Les résul- tats montrent que le seuil de cisaillement du mortier est fortement influencé par la quantité d'eau, par la fines- se et la nature de l’addition minérale, qui modifie aussi la viscosité plastique des mortiers. Le remplacement partiel du sable par des agrégats EPS introduit des valeurs incongrues, causées par la ségrégation, dans le seuil de cisaillement du mortier, tandis que les granulats de liège sont responsables de la réduction du seuil de cisaille- ment du mortier. Key words: cement-based mortar, mineral additions, wastes materials, flowability, rheology © Appl. Rheol. 23 (2013) 15505 DOI: 10.3933/ApplRheol-23-15505 Applied Rheology 15505-1 Volume 23 · Issue 1 1 INTRODUCTION hydrophobic nature of EPS aggregates, it tends to float. This can result in a poor mix distribution The use of mineral additions in cement-based and segregation, requiring the use of bonding mortars offers some significant benefits, from additives [14]. Chen and Liu [15] showed that incor- economical to environmental aspects, including porating fine silica fume, instead of bonding addi- durability related parameters. The reduction of tives can improve the dispersion of EPS in the cement clinker consumption can lower the car- matrix and the interfacial bonding strength. bon footprint, thus contributing to sustainable Beyond the lightweight aggregate most development. Moreover, some mineral additions commonly used, granules of cork have interest- can be obtained from industrial by-products or ed some researchers [16, 17] in order to take wastes that are cheaper than cement. Foremost, advantage of its low thermal conductivity in mor- mortars produced with mineral additions are tar and concrete. To check the influence of dif- often found to perform better in terms of work- ferent additions and aggregates on the fresh ability, strength and durability parameters [1 – 5]. properties of mortars, flow table test or consis- However, it has been found that the incorpora- tency test is widely used. It is simple to perform, tion of some mineral additions has very compli- employs easy-handling equipment, and allows a cated effects, which may either be beneficial or guided evaluation of the influence of fine mate- detrimental, on the flowability of cement paste/ rials addition. In the same way, rheometers have mortar [6]. It is the case of silica fume when used been used [7, 18, 19] in the rheological characteri - in mortars or concrete mixtures that demands a zation of cement based materials with addition- higher water/binder ratio (W/B) or a higher al advantage of measuring simultaneously the amount of superplasticizer (SP) to achieve the apparent viscosity and yield stress for a wide rheological desirable properties in the fresh state range of deformation rates. The rheological [7 – 9]. Due to the fineness of its grains, consis- behaviour of a cement mortar is often described tency of the mortars with metakaolin greatly de - by the Bingham Model [19 – 21]: creases in comparison with the cement reference mortar [10]. In the particular cases of aggressive environ- (1) ments, such as promoted by cyclic freeze-thaw, usually the durability of mortar and concrete is where t(Pa) is the shear stress at shear strain rate g −1 t h improved with the incorporation of fine air bub- (s ) and o (Pa) and (Pa·s) are the yield stress ble [11]. The air-entrained agent is almost always value and plastic viscosity, respectively. These supplied with air contents of about 4 –6%, which rheological parameters can be obtained in rela- in most cases gives a good performing product tive and satisfactory degree of accuracy by test- [12]. Thus, the workability of fresh concrete is sig- ing mortars samples in coaxial cylinders visco - nificantly improved due to the generation of a lot meter. The flow curve can be plotted from the of micro-air bubbles when an air-entraining viscometer data in form of torque T, against agent with high quality is added, i.e., its slump is speedy N and expressed according to the equa- enhanced, but its bleeding and segregating tion: capacity is reduced and therefore the cohesive- ness and homogeneity of concrete are enhanced (2) [13]. Another way to change the voids and de - formability of mortar and concrete is using light- Where, g and h are the constant characteristics weight aggregates. The main problem associat- of the material. The comparison of Equations 1 ed with lightweight aggregates is that these and 2 suggests, in principle, that g is related with porous aggregates absorb a large quantity of the the yield stress and h is related with the plastic mixing water. This absorption by the aggregate viscosity [19]. will mean that additional water will be required The knowledge of mortars rheology may to maintain the workability at acceptable levels. contribute to understand the behaviour of fresh Expanded polystyrene (EPS) beads are a type of materials and can allow predicting their flow artificial ultra-lightweight non-absorbent aggre- properties. Some authors [22, 23] have studied gate. Regarding to extremely lightweight and the correlations between slump, flow table tests Applied Rheology Volume 23 · Issue 1 15505-2 ule of 2.82, density of 2590 kg/m3 and water absorption of 0.43 %. To partially replace the fine aggregates, cork granules, a by-product in the cork industry, was produced in laboratory result- ing in particles with a fineness module of 3.9, density of 250 kg/m3 and water absorption of 4.8 %. A waste granules of expanded polystyrene recycled from packaging materials was also pro- Figure 1: and the parameters obtained by rheometer duced resulting in fineness module of 4.5, densi- Sieve analysis of sand,