The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations.

Ioan Ardelean

doi:10.3390/molecules26175328

Abstract

Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, that this approach inherently assumes that the pores are saturated with water during the hydration process. In the present work, this assumption is eliminated, and the pore evolution is discussed on a more general basis. The new approach is implemented here to extract information on surface evolution of capillary pores in a simple cement paste and a cement paste containing calcium nitrate as accelerator. The experiments revealed an increase of the pore surface even during the dormant stage for both samples with a faster evolution in the presence of the accelerator. Moreover, water consumption arises from the beginning of the hydration process for the sample containing the accelerator while no water is consumed during dormant stage in the case of simple cement paste. It was also observed that the pore volume fractal dimension is higher in the case of cement paste containing the accelerator.

Highlights

Reducing the carbon footprint associated with cement production is an important objective nowadays, and it can be achieved by a better exploitation of the cement composites, for instance, using 3D printing technology [1]
Monitoring the evolution of Nuclear Magnetic Resonance (NMR) relaxation time under the influence of different parameters can be used as a tool in determining the pore evolution of cement-based materials
The approach employed here removes the generally used assumption that the capillary pores are saturated with water during the early hydration

Summary

Introduction

Reducing the carbon footprint associated with cement production is an important objective nowadays, and it can be achieved by a better exploitation of the cement composites, for instance, using 3D printing technology [1]. Building without formworks has the advantage of saving cost, time and materials associated with formwork construction. It implies some significant materials engineering challenges to substitute all the requirements which are typically fulfilled by the formwork. One of the most important characteristics of concrete extrusion, opposite to castable concrete, is that it requires fast-setting and low slump [2]. These requirements must be fulfilled because the material is unsupported after leaving the print nozzle. That is why the cement-based materials for 3D printing applications are designed to exhibit fast build-up process. It is necessary that the mix energy used to break the bounds inside the material should be low to enable delivery by normal pumps [1]

Methods

Results

Conclusion