Limestone and silica powder replacements for cement: Early-age performance

Abstract

Developing functional concrete mixtures with less ordinary portland cement (OPC) has been one of the key objectives of the 21st century sustainability movement. While the supplies of many alternatives to OPC (such as fly ash or slag) may be limited, those of limestone and silica powders produced by crushing rocks seem virtually endless. The present study examines the chemical and physical influences of these powders on the rheology, hydration, and setting of cement-based materials via experiments and three-dimensional microstructural modeling. It is shown that both limestone and silica particle surfaces are active templates (sites) for the nucleation and growth of cement hydration products, while the limestone itself is also somewhat soluble, leading to the formation of carboaluminate hydration products. Because the filler particles are incorporated as active members of the percolated backbone that constitutes initial setting of a cement-based system, replacements of up to 50 % of the OPC by either of these powders on a volumetric basis have minimal impact on the initial setting time, and even a paste with only 5 % OPC and 95 % limestone powder by volume achieves initial set within 24 h. While their influence on setting is similar, the limestone and silica powders produce pastes with quite different rheological properties, when substituted at the same volume level. When proceeding from setting to later age strength development, one must also consider the dilution of the system due to cement removal, along with the solubility/reactivity of the filler. However, for applications where controlled (prompt) setting is more critical than developing high strengths, such as mortar tile adhesives, grouts, and renderings, significant levels of these powder replacements for cement can serve as sustainable, functional alternatives to the oft-employed 100 % OPC products.

Experimental Study of Self-Compacting Mortar Incorporating Recycled Glass Aggregate

“…Limestone powder increases packing density of particles, lowers void ratio and improves durability [43]. Furthermore, it lowers setting time and improves fluidity [44]. In this experimental study, the first charge of water to powder volume ratio (V W /V P ) was considered the same value of β p (retained water ratio) based on recommendation of the Japanese mix design method.…”

Ability of Two Dam Fine-Grained Sediments to be Used in Cement Industry as Raw Material for Clinker Production and as Pozzolanic Additional Constituent of Portland-Composite Cement

“…This hydration acceleration using filler has been reported in literature [87]. This accelerated hydration is explained by the nucleation sites provided by filler addition for C-S-H growth [58,88]. Concerning 900STA and FA, the additional heat due to pozzolanic reaction is only observed after 16-18 h after the beginning of the experiment.…”

Low-temperature curing strength enhancement in cement-based materials containing limestone powder

“…Because mortars containing limestone powder exhibit this low temperature strength enhancement while those without it do not, the focus here will be on the interaction of carbonates with calcium aluminate phases and not on the hydration of calcium silicates to produce C-S-H and calcium hydroxide. While the calcite form of CaCO 3 significantly accelerates early hydration of these silicate phases [4, 6–9, 15], for a system containing the same proportion of CaCO 3 , this acceleration would not offer a viable explanation of low temperature strength enhancement (as in fact the opposite behavior might be expected). Additionally, the reactivity of the ferrite phase (C 4 AF) will not be considered in detail at this first stage of analysis, although the incorporation of iron into carbonate containing AFm phases has been examined previously [16].…”

“…The sustainability-driven quest to replace a significant portion of portland cement in concrete with other materials has led to renewed interest in limestone powders as an effective accelerator of early-age hydration and beneficial modifier of rheology [1–9]. The addition of (calcium) carbonate to the cementitious system changes the phase equilibria and its temperature dependence.…”