Materials Science and Engineering A363 (2003) 152–158 The effects of bond strengths between lightweight and ordinary aggregate-mortar, aggregate-cement paste on the mechanical properties of concrete Metin Husem * Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey Received 21 October 2002 Abstract The interfacial zone between cement paste and aggregate plays a critical role in determining mechanical properties of concrete. In this study, the effects of bond strength between aggregate and mortar, aggregate and cement paste on the mechanical properties of lightweight and ordinary concrete were examined. The flexural and compressive strengths of specimens of lightweight and ordinary mortars, the aggregate used in production of lightweight and ordinary concrete, and pure cement paste were experimentally determined together with the bond strength between aggregate and mortar, aggregate and cement paste. In experimental studies, natural lightweight aggregate and normal aggregate with Portland cement were used. Some basic expressions obtained from using aggregate strength, mortar strength, cement paste, and bond strength were given to estimate the compressive strength of lightweight and ordinary concretes. © 2003 Elsevier B.V. All rights reserved. Keywords: Bond strength; Aggregate; Mortar; Cement paste; Lightweight aggregate; Ordinary aggregate 1. Introduction Concrete is known as a composite material produced by adding the appropriate portions of coarse and fine aggre- gates, cement, water and some additives when necessary [1–3]. It is known that the inhomogeneous structure of con- crete can be described as a three-phase system consisting of hardened cement paste, aggregate and the interface between aggregate and cement paste [4]. At the beginning aggregates, which were forming third-fourths of the concrete compo- sition were accepted as filling materials, while aggregate gradation and its quantity were taken into consideration, its chemical and mineralogical structure did not get so much importance [3]. After the studies, which held concrete as a composite material including various phases were began, the effects of the mechanical properties of aggregates beside cement paste on the concrete behaviour were investigated. Then, researchers started to investigate the type and quality of the relation between aggregates and cement paste which * Tel.: +90-462-377-2622; fax: +90-462-377-2606. E-mail address: mhusem@ktu.edu.tr (M. Husem). form concrete [5,6]. At the beginning, it was thought that there was a mechanical relation between aggregates and cement paste depending solely on surface roughness. In the later studies, it was found that there was a chemical relation between aggregate and cement paste, and the attention to this matter increased [6,8,9]. The researches, which study the strength of the relation, i.e. adherence, between aggre- gate and cement paste are few in number. However, studies on the effects of aggregate-cement paste or aggregate-mortar bond strength on the mechanical behaviour of concrete are much less. Although they are few in number, most of these studies were on ordinary aggregates [10–17]. In these stud- ies, some researchers examined flexural of concrete and its compressive strength, the aggregate-cement paste bond strengths and mortar deflection and compressive strength together, and found that there was a direct relation between concrete strength and others [18]. On the other hand, in some other studies, it was found that there was no effect of the aggregate-mortar bond strength on the compressive strength of concrete [3,7,19]. In this study, the effects of lightweight and ordinary aggregate-mortar, aggregate-cement paste, bond strength on the mechanical properties of lightweight and ordinary 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00595-1