Issue 28, 2021, Issue in Progress

Autoclave-free ultra-early strength concrete preparation using an early strength agent and microstructure properties

Abstract

In this study, nano calcium silicate hydrate was used as an early strength agent to promote the compressive strength of concrete at 1 day. The strength development and the microstructure of standard concrete (SC), autoclave-free ultra-early strength concrete (ESC) and autoclaved concrete (AC) were comparatively studied. The development of hydration products, morphology and pore-structure with ages were investigated via XRD, TG, microhardness, SEM and NMR tests to reveal the mechanism of early strength of ESC. The results showed that the compressive strength of ESC at day 1 achieved 60% of the designed strength, as strong as 45.6 MPa, and only 3% less than that of SC after 90 days. While the compressive strength of AC was significant increased over 90% of ultimate at 1 day, then slightly raised after that. The hydration products did not changed between ESC and SC, but the content of C–S–H gel, Ca(OH)2 and non-evaporated water of ESC was higher in the same specific age. New hydration products such as hydrogarnet and tobermorite were found in AC under autoclave conditions. The microhardness of the paste and ITZ of ESC were also higher than those of SC. The porosity of ESC at 1 day was larger than that of SC, which was contributed by gel pores (1–10 nm). However, AC with higher ratio of large pores than ESC and SC exhibited the largest porosity. The results proved that nano calcium silicate hydrate as an early strength agent significantly increased the early strength of concrete under autoclave-free conditions. Nano calcium silicate hydrate particles supplied additional nucleus in pores and ITZ, accelerated the formation of C–S–H gel, hardened hydration products, and improved the porosity structure. However, with autoclave curing, the hydration products in AC formed with larger size and higher crystallization, which benefited for early strength. However, the large porosity with large size pores might cause damage.

Graphical abstract: Autoclave-free ultra-early strength concrete preparation using an early strength agent and microstructure properties

Article information

Article type
Paper
Submitted
01 Mar 2021
Accepted
23 Apr 2021
First published
12 May 2021
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2021,11, 17369-17376

Autoclave-free ultra-early strength concrete preparation using an early strength agent and microstructure properties

D. Sun, Z. Wang, R. Ma, A. Wang and G. Zhang, RSC Adv., 2021, 11, 17369 DOI: 10.1039/D1RA01611C

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements