Date Published: April 26, 2019
Publisher: Public Library of Science
Author(s): Yan Feng, Qinli Zhang, Qiusong Chen, Daolin Wang, Hongquan Guo, Lang Liu, Qixing Yang, Kedsarin Pimraksa.
This study aims at evaluating the effect of ultrafine granulated copper slag (UGCS) on hydration development of blended cement and mechanical properties of mortars. The UGCS with the median particle size of 4.78 μm and BET surface area of 1.31 m2/g was used as a cement replacement to prepare blended cements. Hydration heat emission of blended cement and mechanical performance of mortars were investigated by using isothermal calorimetry and strength tests, respectively. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were applied to the analysis of pozzolanic reaction and hydration products. The results illustrate that UGCS has influence on the hydration heat evolution of blended cement due to its filler effect and pozzolanic reaction. The cumulative hydration heat of blended cement is reduced by partial cement replacement with UGCS. The test mortar prepared by using blended cements with 30 wt. % UGCS shows a retardation of strength development with a low value at early ages (7 days) and a rapid growth at later ages (28 days). The 90-day compressive strength of test mortar is 45.0 MPa close to that of the control mortar (49.5 MPa). The obtained results from XRD and TGA analysis exhibit an increase in calcium hydroxide (CH) consumption and calcium silicate hydrates (C–S–H) formation in blended cement pastes with curing time. The cement replacement with UGCS induces changes in microstructure of blended cement paste and chemical composition of hydration products.
Recently, the utilization of industrial by-products as supplementary cementitious materials (SCMs) in cement and concrete has attracted considerable attention for the technological, economic, and environmental benefits [1–4]. Copper slag is a by-product generated from the process of copper manufacturing . Granulated copper slag (GCS) is an amorphous material due to rapid water cooling, in which the glassy phase consists mainly of ferrous oxide (FeO), silicon dioxide (SiO2), and minor amount of other compounds . The high content of reactive SiO2 in GCS endorse its latent pozzolanic properties . Nevertheless, the low activity of GCS adversely affects the mechanical performance of cement and concrete at early ages when used as partial substitution of cement [8,9].
Portland limestone cement (PLC) used in the present study was CEM Ⅱ/A-LL 42.5 R and copper slag was provided by a copper smelter via water granulation of liquid slag from the settling furnace. The as-received slag was screened by standard sieves and the feedstock particles with fineness below 150 μm in diameter were obtained. High-energy milling test was carried out in a vibrating mill (Humboldt, Germany) with a vibrating amplitude of 10 mm and a frequency 1000 rpm. The milling was performed using cylpebs with a diameter of 12 mm for duration of 3 h and the UGCS in this study was obtained.
Hydration and strength development in blended cement with ultrafine granulated copper slag (UGCS) were investigated by using isothermal calorimetry and compressive tests. XRD, DTA/TGA, and SEM were applied to the analysis of pozzolanic reaction and hydration products. The conclusions can be summarized as follows: