Effect of Calcium Nitrate on the Properties of Portland-Limestone Cement-Based Concrete Cured at Low Temperature.

Asta Kičaitė,Ina Pundienė,Harald Justnes,Gintautas Skripkiūnas

doi:10.3390/ma14071611

Asta Kičaitė, Ina Pundienė + Show 2 more

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https://doi.org/10.3390/ma14071611

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Abstract

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

Highlights

Published: 25 March 2021Concrete is a composite material made up of cement matrix and aggregates
The results reveal that 1% calcium nitrate (CN) alone acts as acts as an accelerating admixture; it has only a minor positive impact on the an accelerating admixture; it has only a minor positive impact on the long-term long-term growth of mechanical strength, which is confirmed by Polat [18,47]
For the samples with CN contents of 1, 2, and 3%, the compressive strength results were 6.9, 13 of1.9, and 12.8% higher, respectively, compared to the samples that were not kept at low temperatures

Summary

Introduction

Concrete is a composite material made up of cement matrix and aggregates. The gel, which is formed during the reaction between cement and water, solidifies and binds the aggregates. The most common binders for concrete are various types of Portland cements. The cement industry relates to 5–8% of total human. One ton of cement produces about 900 kg of CO2 [4]. In this case of blended cements, energy losses and carbon footprint are reduced [5,6]. The partial replacement of Portland cement with mineral additives in concrete has been used for a long time

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