Effect of Additional Surfaces on Ordinary Portland Cement Early-Age Hydration

Tapio Vehmas,Andrzej Cwirzen,Anna Kronlöf

doi:10.4236/msa.2017.812063

Abstract

Early-age hydration of Ordinary Portland Cement (OPC) was studied in the presence of two additional surfaces. Additional surfaces are known to accelerate the early-age hydration of OPC. Autocatalytic reaction modelling was used to determine acceleration mechanism of additional surfaces. Heat development of the hydration was measured with semi-adiabatic calorimetry and the results were modelled with an autocatalytic reaction. Autocatalytic reaction modelling was able to determine number of initially active nucleation sites in early-age hydration. OPC hydration followed autocatalytic reaction principles throughout induction period and accelerating period. Both of the added surfaces, limestone filler and calcium-silicate-hydrate (C-S-H) coated limestone filler accelerated the early-age hydration. According to autocatalytic modelling, the C-S-H coated filler increased the number of initially active nucleation sites. Pristine limestone filler accelerated the early-age hydration by providing the additional nucleation sites throughout the early-age hydration. The difference was explained with common theories of nucleation and crystal growth. Autocatalytic model and measured calorimeter curve started to significantly deviate at the inflection point, where the reaction mode changed. The reaction mode change depended on the average particle distance. Early-age hydration, modelled as autocatalytic reaction was able to improve understanding of OPC early-age hydration and quantify the number of initially active nucleation sites. Understanding and quantifying the acceleration mechanisms in early-age hydration will aid larger utilization of supplementary cementitious materials where understanding the early-age strength development is crucial.

Highlights

In recent decades, nucleation and crystal growth mechanisms has received an ever strengthening position as the explanation of hydration phenomena of Ordinary Portland Cement (OPC) [1]
Heat development of the hydration was measured with semi-adiabatic calorimetry and the results were modelled with an autocatalytic reaction
The application of the autocatalytic model to the heat output revealed that the quantity of the initial C-S-H, [B0] increased as the water/cement-ratio (w/c) increased (Figure 4)

Summary

Introduction

Nucleation and crystal growth mechanisms has received an ever strengthening position as the explanation of hydration phenomena of Ordinary Portland Cement (OPC) [1]. Application of classical crystal growth theories [3] [4] failed to explain slow hydration during the induction period without additional hindering process. This hindering process has been explained with formation of membranes with meta-stable layers and their later rupture. Thomas adapted a modified Avrami crystal growth model [3] and successfully explained the origin of the induction period as a part of a crystallization process, without a need for additional hindering mechanism. Further evidence for nucleation models were gained from addition of artificial growth sites of calcium-silicate-hydrate by Thomas et al, in the form of a pre-precipitated calcium-silicate-hydrate (C-S-H) [15]

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Conclusion