Elsevier

Construction and Building Materials

Volume 98, 15 November 2015, Pages 44-50
Construction and Building Materials

Assessing the pozzolanic activity of cements with added sugar cane straw ash by synchrotron X-ray diffraction and Rietveld analysis

https://doi.org/10.1016/j.conbuildmat.2015.08.103Get rights and content

Highlights

  • Sustainability is the key word in the development of new technologies.

  • The use of alternative materials in the cement paste is focused.

  • Cement pastes and cement pastes blended with Sugar Cane Straw Ashes were studied.

  • Our findings contribute in the phase identifications of cementitious pastes.

  • The pozzolanicity of the agroindustrial wastes was proven using synchrotron radiation.

Abstract

Sugar and alcohol industries generate large amount of wastes that could produce ashes of great reactivity with pozzolan properties. The objective of this paper is to evaluate the pozzolanicity of Sugar Cane Straw Ashes (SCSA), thermal treated, at different curing times. Employing Synchrotron X-ray radiation for XRD measurements, scans from 10° to 110° (θ-2θ setup) allowed the quantification of several phases of the cement pasts through Rietveld analysis. The SCSA substitution of 20% (weight) in Ordinary Portland Cement (OPC) has improved the AFt (Ettringite) formation up to 47% for 90 days curing time. The Portlandite concentration analysis allowed concluding that this addition of SCSA in OPC has caused a delay in the cement setting time. Moreover, the behaviour of the C3S and Calcite contents in both OPC and OPC/SCSA samples were determined by refinement of the XRD pattern using the Rietveld method.

Introduction

Industrial production of cement in Brazil started in 1920, reaching a maximum of 40.2 million tones in 1999 [1]. Despite of a series of up and downs due to economic upheaval, another peak of 65 million tons was attained in 2011. Preliminary information about cement consumption on April 2013 reached 5.9 million of tons [2].

Nowadays, the Brazilian cement industry is among the 10 largest cement world producers and consumers, has a modern industrial park, is internationally recognised for recycling waste minerals and by preserving the environment (low CO2 emissions) and also by the use of biomass for power generation. Despite these mitigating factors, the expansion of construction activity in Brazil motivates the search for materials that can replace cement. This replacement is necessary due to the environmental and social impacts caused by the production of cement.

Researches involving the use of pozzolans in cementitious matrices have increased significantly in recent years. In the absence of natural pozzolan, cement industries look for new materials in agroindustry. Several authors have reported the use of agroindustrial ashes to partially replace Portland cement [3], [4], [5], [6], [7].

The use of sugar cane straw, as forage, contributes to decrease the soil erosion and to reduce the carbon emission from soil to atmosphere [8]. Furthermore, the wastes of sugar cane production can be recycled by biorefinaries to get energy with a substantial generation of ashes. Since Brazil is the world’s largest producer of sugar cane having a huge organic by-products surplus of bagasse and straw [8], [9] has a strong interest in finding a way to recycle this waste. One possible solution could be its combustion. Indeed, some authors have reported that these wastes when burned under controlled temperature may show high reactivity, reacting as a pozzolanic material [10], [11].

To assess a pozzolanic material it is necessary to carry out a complete series of chemical, physical and mechanical tests to evaluate its performance. One of them involves the direct identification of calcium silicate hydrates (CSH) phases, promoted by pozzolanic reaction, as a function of time [12], [13], [14] up to ninety days. This can be carried out by X-ray diffraction, quantifying both the initial crystalline phases and the hydration products over long periods (months), since the pozzolanic reaction is normally slow.

The aim of this paper, consequently, is to evaluate the pozzolanic reaction in blended cement pastes, both without (control) and with sugar cane ashes added, treated at 700°C, for periods of three, seven, twenty-eight and ninety days. To achieve that, synchrotron X-ray diffraction data acquired at the Brazilian facilities of LNLS, have been studied and crystalline phases quantified by Rietveld analysis in order to have a picture of the major phases evolution during the cement pastes hydration.

Section snippets

Sugar Cane Straw Ashes (SCSA)

The sugar cane straw was harvested from Centro de Tecnologia Canavieira (CTC), placed at Piracicaba, São Paulo – Brazil. It was collected directly from the ground and exposed to the natural environment to naturally dry for 24 h. The ash was obtained from the burning control in an electrical furnace with 10°C/min heating rate during 3 h at 700°C X(hereafter SCSA). The production of the ashes was divided in two levels in order to obtain a homogeneous burning, according to Fig. 1. On reaching the

Chemical and physical characterisation of SCSA

The chemical composition and LOI of the ash are shown in Table 1. A pozzolan should present in its chemical composition silica as the predominant phase and at least 50% of the sum of the oxides: SiO2, Al2O3 and Fe2O3. The presence of certain chemical elements such as sodium and potassium may be undesirable, because they provoke alkali-aggregate reaction in the cement matrix. The SO3 content should be a maximum of 5% [16]. The chemical composition of SCSA is presented in Table 1, contain 61.0%

Conclusions

The objective of this paper is to investigate important issues such as ash addition in OPC, the effect of curing time in pure Ordinary Portland Cement (OPC) and Sugar Cane Straw Ashes (OPC/SCSA – @700 °C), that needs to be studied to evaluate its industrial applicability. The idea of introducing agroindustrial wastes, as sugar cane ashes into the OPC, opens a wide field of applicability. Therefore, it is necessary to know its behaviour according to the mineralogical variability.

The existence and

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