Durability of Mortars Modified with Calcined Montmorillonite Clay

Abstract

This study aims to evaluate the performance of mortars containing locally available Pakistani montmorillonite (Mmt) clay mineral as partial replacement of cement in various curing environments. The local montmorillonite clay in “As is” (20°C) and “heated” (100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C & 1000°C) conditions was incorporated in mortar cubes as partial replacement of cement. Montmorillonite clay of all the temperatures was replaced by 15%, 20%, 25%, 30% and 35% of cement mass in mortar cubes. The Strength Activity Index (SAI) was calculated to determine the optimum activation temperature for the clay. Compressive strengths of the controlled mix and montmorillonite modified mortars were evaluated under the Sodium Sulfate (SS) (5% solution) and mixed (Sodium Sulfate + Sodium Chloride (SCS)) (5% +3.5% solution) curing environments to study its durability performance. Upon thermal treatment montmorillonite clay showed maximum activation at 800°C temperature. Mortar containing (800°C) calcined montmorillonite clay with 25% cement replacement exhibit competent compression results. Moreover, up on exposure to aggressive environments, montmorillonite clay mortars performed better than the control samples. The mortar cubes exposed to Sulfate environment (SS) were more damaged in compression than that exposed to mixed environment (SCS), for all replacement levels and time exposures.

Thermally Activated Bentonite As a Supplementary Cementitious Material – A Review

“…At relatively low replacement levels (3 -15%), no reductions in compressive strength were reported at all ages [7,14,16].Moreover, significant increases in compressive strength were reported at (3-10% replacement at 28 days [14,16]. `…”

“…At 20% cement replacement, the strength activity indexes at 7 and 28 days were reported at different activation temperatures: 70 and 85% respectively at 500°C [13], 93 and 94% respectively at 800°C [14], and 101 and 104% respectively at 150°C [15]. At early ages of mortars (28 days or less), and replacement levels more than 20%, significant reductions in compressive strength were reported and the reduction increases as the replacement increases [3,9,14,15]; but the reduction in compressive strength disappears at later ages (56 -90 days) or is reversed into an increase at 30% replacement [3,9].…”

“…Because of pozzolanic reaction and pores refinement, TAB improves the durability of cement mortar against alkali-silica reaction at 30% replacement [9] and sulfates attack at 20% replacement [14]. The depth of carbonation of mortar contains 30% TAB is twice the carbonation depth of reference mortar [9].…”

The Influence of Thermo-Mechanical Activation of Bentonite on the Mechanical and Durability Performance of Concrete

“…Mielenz et al [43] studied thermal treatment effect on the pozzolanic reactivity of 70 different types of pozzolana and reported the optimum activation temperature range of 650-870 • C. In previous studies, the optimum activation temperature for Bentonite was reported as the range of 800-830 • C [28,31]. In our previous research [34], the optimum activation temperature of the bentonite clay was found to be 800 • C. Many studies have been conducted in Pakistan for utilizing industrial wastes, such as bagasse ash [44], rice husk ash [45], fly ash [46,47], etc., as SCMs. Some natural pozzolana have also been studied [3,13].…”

“…Bentonite clay fulfills all the requirements of ASTMC-618C [33] to be used as a cement replacement material, as shown in Tables 1 and 2. Moreover, by heating this clay, its pozzolanic reactivity can be enhanced further compared to unheated condition [31,34]. By using bentonite clay as a supplement to OPC, an eco-friendly, economical, and durable concrete can be achieved [3,13].…”