Influence of sodium gluconate on the performance and hydration of Portland cement

doi:10.1016/j.conbuildmat.2015.05.068

Construction and Building Materials

Volume 91, 30 August 2015, Pages 138-144

https://doi.org/10.1016/j.conbuildmat.2015.05.068 Get rights and content

Highlights

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The optimum dosage of Na-gluconate was 0.03% for the compressive strength.
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Na-gluconate reduces the amount of water required, and prolongs setting times.
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Na-gluconate delays the hydration of C₃S, prolonging the induction period.
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Less than 0.03% Na-gluconate promotes the formation of AFt.
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1.0% Na-gluconate inhibites the dissolution of CaSO₄·2H₂O and formation of AFt.

Abstract

Sodium gluconate is commonly used to delay the setting of cement and concrete. This study investigated the effects of sodium gluconate on the physical properties and structure of Portland cement. Sodium gluconate improved the compressive strength at 3 and 28 days, delayed cement setting and increased the fluidity of the Portland cement mortar. Less than 0.03% sodium gluconate promoted the formation of ettringite (AFt) at early age. A dosage of 1.0% sodium gluconate significantly inhibited the reaction between C₃A and CaSO₄·2H₂O. Sodium gluconate delayed the hydration reaction of C₃S, which increased the duration of the induction period. Sodium gluconate had only a slight effect on the hydration reaction of the ferrite phase. The pore distribution and porosity of the cement paste were not improved due to the decrease in hydration.

Introduction

Sodium gluconate is a crystalline powder that can be produced under properly controlled conditions. It is widely used in industry. It can be utilized as a chelating agent in buildings, textile printing and dyeing, metal surface treatment and water treatment, as a cleaning agent for steel surfaces and glass bottles and as a retarder for concrete. Concrete is the largest class of manufactured materials. It comprises cement, aggregates, admixture and water. One of the most common types of admixture in concrete is a superplasticizer admixture. Many studies [1], [2], [3] have shown that the combination of sodium gluconate with a superplasticizer has a significant effect on the slump loss and fluidity of concrete because sodium gluconate has a good retardation action [4]. With respect to the retardation mechanism of sodium gluconate, there are several popular explanations as followed: (1) the formation of AFt is inhibited by the adsorption of gluconate or the complex between gluconate and calcium ions (Ca²⁺) on the surface of C₃A [5], [6], [7], [8]; (2) low concentrations of gluconate can block the nucleation and/or growth of hydration products [9], [10]; (3) the retardation action of gluconate may occur via adsorption on the surface of the silicate phase [11]. However, the improper use of sodium gluconate often causes abnormal setting and large slump losses [12], which results in great economic loss. It was reported that there was a threshold dosage of gluconate needed to obtain cement fluidity after five minutes of hydration [11]. However, the threshold dosage has not been precisely determined. The work described in this paper aims to answer the following questions:

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What is the threshold dosage of sodium gluconate necessary to increase fluidity?
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How do hydrate products develop in the cement paste with sodium gluconate?
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What on earth is the retardation mechanism of sodium gluconate?

Section snippets

Raw materials

The materials used in the experiments included conventional Portland cement, standard sand and sodium gluconate. The chemical compositions of the cement, which was obtained from the Yangzhou Yadong Cement Co. Ltd., are shown in Table 1. The surface area of the cement was 360 m²/kg measured by Blaine method. The cement was a mixture of the clinker, gypsum and fly ash. The mineral compositions of the clinker are shown in Table 2. The standard sand (Chinese Standard GB/T17671) was obtained from

Compressive strength

Fig. 1 shows the compressive strength and rate of strength development for cement mortars. Sodium gluconate enhances both the early strength and late strength, with the exception of the 0.05% dosage (see Fig. 1(a)). The optimum dosage of sodium gluconate is 0.03% for conventional Portland cement, as assessed by the strength of the cement mortar. The compressive strengths are increased by approximately 10% and 6% respectively at 3 and 28 days, compared to the blank cement mortar. The compressive

Discussion

The above results show that sodium gluconate is not only a good retarder but also a good water reducer. Its retardation on the setting times is attributed mainly to delaying the hydration of C₃S in the Portland cement. Perez [9] hypothesized that sodium gluconate would rather adsorb directly onto C₃S dissolution sites than chelate with Ca²⁺ or silica to block its hydration. A small amount of sodium gluconate could promote the formation of AFt. However, when its dosage reaches to 1.0% by weight

Conclusions

The optimum dosage of sodium gluconate in terms of the compressive strength of the cement mortar at 3 and 28 days was 0.03%. The compressive strengths increased by approximately 10% and 6% compared to the blank cement mortar at 3 and 28 days, respectively. A small amount of sodium gluconate favored the initial strength, whereas an excess of 0.03% sodium gluconate favored the late strength.

Sodium gluconate is both a good setting retarder and a strong water-reducing agent. It can significantly

Acknowledgements

The authors are grateful for the financial support of the National Natural Science Foundation of China (51202109), a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and National Building Materials Industry Technology Innovation Programme (2013-M1-1). The support by the facilities of the Modern Analysis and Testing Centre at Nanjing Tech University, where the detailed microstructural analyses were performed, are also acknowledged.

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View full text

Influence of sodium gluconate on the performance and hydration of Portland cement

Highlights

Abstract

Introduction

Section snippets

Raw materials

Compressive strength

Discussion

Conclusions

Acknowledgements

Cem Concr Res

Cem Concr Res

Cem Concr Res

Effect of sodium gluconate on the fluidity and flow loss of pastes with β-naphthalenesulfonic acid-based superplasticizer

J Chin Ceram Soc

Interactions between polycarboxylate superplasticizers and components present in ultra-high strength concrete

J Chin Ceram Soc

Effects of two retarders on the fluidity of pastes plasticized with aminosulfonic acid-based superplasticizers

Constr Build Mater