Polycarboxylate/nanosilica-modified quaternary cement formulations – enhancements and limitations

Abstract

2The effect of polycarboxylate/nanosilica (nS) particles in quaternary cement formulations comprising Portland cement (PC), limestone powder (LS) and fly ash (FA) was investigated for the first time. The reference formulation contained 60% PC, 20% LS and 20% FA by mass of binder in an effort to minimise clinker and maximise the other constituents. nS particles were characterised by way of transmission and X-ray scanning electron microscopy (SEM). The nS was added at 0·3 or 0·6% by mass as a partial replacement for PC and different water-to-binder (w/b) ratios were explored. Compressive strength tests and thermal gravimetric analyses (TGA) performed at day 7, 28 and 56 testified to pozzolanic behaviour. Results suggest a mechanism of 'de-activation' of some FA particles with age. A new ratio: (compressive strength in MPa)/(calcium hydroxide content detected by TGA) was introduced, correlating microscale characteristics (hydration products) and macroscale performance (delivered compressive strengths). Back-scattered SEM images confirmed the calcium-silicate-hydrate (C-S-H) network formation, the presence of reacted/unreacted FA particles and the availability of calcium hydroxide for delayed hydration reactions. Tests on mortars also confirmed the enhancement offered by nS addition. The lower bound nS addition was determined to be 0·6% by mass of binder for pastes and 0·5% for mortars.Notation D relative density m a mass of specimen in air m w apparent mass of specimen immersed in water w/b water-to-binder ratio ρ w density of water

Optimization of Low-Carbon Footprint Quaternary and Quinary (37% Fly Ash) Cementitious Nanocomposites with Polycarboxylate or Aqueous Nanosilica Particles

“…where y % of μS solids by mass, ranging from 2.0% to 5.5%, and x % of nS solids by mass, ranging from 0 to 1.0%. e mixing procedure, casting, demoulding, and curing are described elsewhere [7,10]. In general, dry mixing of the powders took place rst, with a spatula by hand.…”

“…e exact same experimental procedure (TEM and SEM/ EDX) was followed for the characterization of GnS. Images and analyses can be traced in the literature [10].…”

“…Buoyancy effects were taken into account, by correcting the curves via automatic blank curve subtraction. ree different areas are compared, depending on the hydration products thermally decomposing between specific temperature ranges, as measured by the thermogravimetric (TG) analyses [9,10]: e first one is related to the dehydration of C-S-H, ettringite, gehlenite, and monosulfate, between 100°C and 200°C. It can be postulated that the greater the loss measured, the greater the amount of C-S-H and ettringite produced by the hydration of the paste.…”

“…Others studies led by the authors of the present paper suggest that cementitious composite pastes and mortars comprising of 60% PC and 40% LS can be further enhanced by the addition of just 0.5% nS by total mass of solids in terms of mechanical strength and additional hydration reactions [7][8][9]. Moreover, it was found that cementitious composite pastes and mortars containing 60% PC, 20% FA, and 20% LS can be further enhanced by the addition of just 0.5% nS by total mass of solids [10]. In this publication, strength gain was linked to Ca(OH) 2 consumption towards the production of additional C-S-H in a single graph, which can assist in future formulation design.…”

“…ree phases are distinguished: (i) the dehydration of C-S-H, ettringite, and monosulfate occurring approximately between 100°C and 180°C; (ii) the dehydration of Ca(OH) 2 taking place approximately between 400°C and 500°C; and (iii) the decomposition of CaCO 3 between 600°C and 800°C. e technique is o ering an approximation of the C-S-H produced, the Ca(OH) 2 consumed, the extent of pozzolanic reaction, and evidence of carbonation of the samples [7,10,[13][14][15]. e temperature ranges were selected after a further search in the literature, from which a tabulated literature review on TGA was also developed.…”