Construction and Building Materials 220 (2019) 253–266 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Investigate the influence of expanded clay aggregate and silica fume on the properties of lightweight concrete ⇑ Muhammad Riaz Ahmad a,b,c, Bing Chen a,b, , Syed Farasat Ali Shah a,b a State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China b Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China c Department of Civil Engineering, Muhammad Nawaz Sharif University of Engineering and Technology, Multan 60000, Pakistan highlights Energy efficient concrete with environmental impact was produced. The expanded clay aggregate and foam was used to produce thermal mass concrete. Lightweight concrete exhibited higher indoor thermal comfort properties. Produced concrete provided the balance between thermal and structural performance. article info abstract Article history: This study concentrated on the formulation of self-flowing and an energy efficient lightweight aggregate Received 29 December 2018 foamed concrete (LAFC) to be employed as thermal insulation, thermal mass and structural material. Low Received in revised form 14 May 2019 density concrete mixtures (for the density values from 800 to 1300 kg/m3) were prepared by changing Accepted 28 May 2019 the volume of lightweight expanded clay aggregate (ECA) from 49.4% to 20.1%. Flowing properties of con- Available online 10 June 2019 crete mixtures were improved with the help of stable foam. Ordinary Portland cement (OPC) was replaced by the 5% and 10% silica fume (SF) to examine the influence of SF on the properties of LAFC. Keywords: Compressive strength and tensile strength of LAFC mixtures were respectively enhanced from 6.5 MPa Foamed concrete to 24.30 MPa and 0.52 MPa to 1.63 MPa by reducing the volume of ECA from 49.4% to 20.1%. LAFC mixture Expanded clay aggregate Porosity (800-0SF) with the lowest density exhibited highest porosity and sorption coefficient value of 70.63% and À2 À0.5 Sorptivity 2.56 kg m min . Thermal conductivity, volumetric specific heat capacity and thermal diffusivity of À1 À1 3 2 Thermal conductivity LAFC mixtures were in the range of 0.23–0.45 W m K , 1136–1631 kJ/m .K and 0.20–0.275 mm /s respectively. SEM analysis revealed that reduction in the volume of ECA and addition of SF densified the microstructure of LAFC. Finally, LAFC mixtures were classified into Class-I, Class-II and Class-III grade concretes for the structure and insulation purposes as per functional classification of RILEM. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction bility and energy efficiency of buildings can be increased through the improvement in thermal properties of construction materials. Due to the scarcity of available energy resources, a lot of A lot of previous studies have examined the workability, researches are being conducted on the usage of energy saving mechanical, thermal and hygroscopic properties of lightweight and energy efficient materials, and some countries have included concrete containing foam and lightweight aggregate. Lightweight the use of these materials in their fundamental policy to conserve concretes, foamed concretes and aerated concretes with excellent the natural resources. In China, construction industry nearly con- thermal properties have been used as exterior wall materials sumes 35% of total energy [1]. In the modern day, construction [2–9]. Foamed concrete belongs to the family of lightweight con- industry is rapidly growing industry because of the peak demands crete and it is mainly composed of Portland cement (OPC), foaming of contemporary infrastructure. In such cases, environmental sta- agent, and aggregate. The purpose of using foaming agent is to introduce entrapped air in lightweight concrete [10]. Generally, mechanical properties of Lightweight aggregate foamed concrete ⇑ Corresponding author at: State Key Laboratory of Ocean Engineeing, Shanghai (LAFC) are inferior to normal weight concrete (NWC), but it can Jiao Tong University, Shanghai200240, PR China. be employed as partition and load-bearing walls for the low-rise E-mail address: [email protected] (B. Chen). https://doi.org/10.1016/j.conbuildmat.2019.05.171 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. 254 M.R. Ahmad et al. / Construction and Building Materials 220 (2019) 253–266 buildings [5,11,12]. Opposite to normal weight concrete, Light- weight aggregate foamed concrete can be also used for thermal insulation, void filling, vibration attenuation and dead load reduc- tion. Recently, foam concretes have been formulated with the wide range of densities (300–1600 kg/m3), compressive strength (0.3– 30 MPa) and thermal conductivities (0.2–0.8 WmÀ1 KÀ1) [4,6,13,14]. Lightweight aggregate concrete (LWAC) mainly improves the thermal and sound insulation properties of buildings beside its structural applications. Lightweight aggregate used in the LWAC should conforms to ASTM C330 [15] and 28 days compressive strength of LWAC should be at least 17 MPa with the density in the range of 1120–1920 kg/m3 [16]. LWAC concrete can be pre- pared either by using naturally available lightweight aggregate or artificially made lightweight aggregate. Artificial LWA are normally Fig. 1. Proportion of measured thermal properties of cement and concrete k b produced by using the natural raw materials or byproducts [15]. ( – thermal conductivity, Cp – specific heat capacity, – thermal diffusivity). Expanded clay aggregate (ECA) is a type of artificially produced LWA that is formed by expanding the natural clay at a high tem- agent tends to form micropores inside the concrete. A stable foam perature of around 1200 °C in a rotary kiln [17–19]. The particles was used to improve the homogeneity and avoid the segregation shape of ECA is spherical with they have a closed and barely porous and bleeding of lightweight concrete. The produced concrete outer surface as compared to inner structure that is black in the demonstrated considerably superior thermal and mechanical prop- color and highly porous. Previously ECA has been used to prepare erties as compared to previous studies for the same range of den- lightweight masonry plaster and mortar [20,21], self-healing con- sity. Mix design of concrete was carried out for the different crete [22], structural lightweight and self-compacting concrete volume of expanded clay lightweight aggregate (ECA) ranging from [7,12], as a filler in aluminum tubes [23], and for the thermal insu- 20.1% to 49.4%. SF was also incorporated to check its effect on the lation purposes [7]. In the traditional concrete, strength of normal properties of LAFC. Workability, mechanical, thermal, hygroscopic weight aggregate is generally higher as compared to interfacial and microstructural properties of LAFC were investigated for the transition zone (ITZ) and matrix. However, LWA acts as a weakest characterization purpose. source of strength in the LWAC and it can significantly affect the elastic and mechanical properties of lightweight concrete [24]. Past studies investigated the aggregates properties and their effects on 2. Materials and methods the properties of concrete. It was reported that weakest compo- nent of the concrete determines its strength. If aggregate is stron- 2.1. Raw materials gest component of concrete mixture, forces are transferred through the aggregate and matrix. However, stress is transmitted through Several LAFC mixtures were prepared by mixing the following the cement matrix and cracks are spread through the aggregate if raw materials; ordinary Portland cement (OPC) as cementitious LWA is weakest constituent in comparison with matrix. Hence, it materials, ceramsite based expanded clay aggregate (ECA) as light- was concluded that LWA is a weakest link as compared to ITZ in weight aggregate, uncompacted silica fume (SF), animal protein- the LWAC [25–27]. based foaming agent, Polycarboxylate superplasticizer (SP) and Production of lightweight concrete having the self-flowing water. SP was in the solid form with the chloride content less than 3 properties is a challenging task when employing the high propor- 0.20%, pH value of 9.0 ± 0.2, bulk density value of 550 kg/m , water tion of lightweight aggregate. The formulated concrete mixtures reduction rate of 20% and completely soluble in the mix. Ordinary are prone to segregation and bleeding. Lightweight concrete with Portland cement (OPC) with a 28-day compressive strength of the density in range of 800–1300 kg/m3 are normally used only 55.5 MPa was used. The silica fume was obtained from Elkem for insulation purposes due to their lower mechanical properties Materials Co., Ltd with a SiO2 content of 92.4%. ECA made by heat- as compared to normal weight concrete. Most of the studies ing around 1200 °C was transported from Shandong province of focused of lightweight concrete to be used either as structural China. Photograph and SEM images of SF, cement, foam and ECA materials having high strength or non-structural materials having are shown in the Fig. 2. It can be observed that ECA exhibits highly low thermal conductivity. The balance between the thermal and porous structure. The chemical composition of OPC and SF is given mechanical properties is not discussed. Also, the available knowl- in the Table 1. The physical properties of lightweight aggregate are edge regarding the thermal properties of lightweight aggregate given in Table 2. concrete is not sufficient. It can be observed from the Fig. 1 that high proportion of studies have investigated only thermal conduc- 2.2. Mixtures preparation tivity of cement and concrete in details [28]. Contrarily, there are only few studies are available on the thermal properties (volumet- LAFC mixtures were prepared by mixing the OPC, SF, ECA, foam- ric specific heat capacity or thermal mass, thermal diffusivity and ing agent, superplasticizer and water in various proportions. Four thermal resistivity). Hence, the main objective of this research is mix proportions were designed to prepare the foamed concrete to formulate self-flowing and an energy efficient low-density light- of different densities.