Evaluation of mechanical properties of lime-pozzolan concrete containing silica fume, blast furnace slag and zeolite

Document Type : Original Research

Authors
A. arabzadeh 1
A. ahmadi 2
1 Associate Professor of Civil Engineering, Faculty of Civil and Environmental Engineering, Tarbiat Modares University
2 Master student of Structural Engineering, Faculty of Civil Engineering and Environment, Tarbiat Modares University
DOI: 10.22034/22.3.7
Abstract
Growing apprehension about the environmental effects of producing Portland cement as the main component of the concrete, has raised widespread concerns in construction industry about the urgency of finding appropriate materials to substitute it. Recently, lime-pozzolan binders that were used before the advent of Portland cement, have been revived and reconsidered in a quite modern way showing reliable properties.

In this study, according to past research on lime-pozzolan concrete, with the aim of producing concrete having dominant lime-pozzolan binder with desirable structural properties, different lime-pozzolan concrete mixes with double and triple compounds of hydraulic lime with silica fume, blast furnace slag and zeolite and two mixes with the presence of 30% Portland cement in lime-pozzolan concrete were made and tested. In all mixes, the super-plastisizer admixture was used to improve the concrete workability. To gain the most concrete strength, a constant water to binder ratio of 0.35 was used for manufacturing all concretes specimens except the one containing zeolite in which water to binder ratios lower than 0.45 wasn’t practical. Portland cement binder concrete were manufactured as well for comparing purposes. Slump test was conducted on fresh concrete and compressive strength test on cubic molds (10×10×10 cm) in 7, 28 and 56 days, spilling tensile strength test on cylindrical molds (with a diameter of 10cm and a height of 20cm) in 28 days, flexural strength test on prismatic templates (10×10×35 cm) in 14 and 28 days and elastic modulus test on cylindrical molds (with a diameter of 10cm and a height of 20 cm) in 28 days was conducted on hardened concretes. To analyze pozzolanic activity,the Thermal Gravimetric Analysis (TGA) was performed on concrete samples which showed better strength results than others.

Slumpchr('39')s results show that the use of the super-plastisizer in the lime-pozzolan concrete improves their workability; Most slumps were obtained in lime-slag-silica and lime-slag-cement concrete at 22 and 23 mm, respectively. Four mixes of lime-pozzolan concrete (two mixes with 50% natural hydraulic lime (NHL) composition and 30% cement with 25% silica fume (SF) or 25% ground granulated blastfurnace slag (GGBS) and two other triple mixes 50% NHL, 25% SF and 25% GGBS and dual mixes 70% NHL with 30% SF) showed competitive mechanical properties compared to ordinary concrete and their 28-day compressive strength were achieved above 30 MPa (Equivalent to 58.6, 40.2, 40.1 and 33.5 MPa, respectively), which is quite favorable to be used as structural concrete. Concrete containing zeolite had less mechanical strength than others.

The results of thermal gravimetric analysis were determined in the lime-pozzolan concrete, more calcium hydroxide is consumed as the amount of pozzolan increases. Silica fume performed more active than blast furnace slag, because it consumed more calcium hydroxide in concrete. Also blast furnace slag was more active than zeolite.

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Modares Civil Engineering journal
Volume 22, Issue 3
May and June 2022
Pages 7-20