Basalt waste added to Portland cement

Portland cement is widely used as a building material and more than 4.3 billion tons were produced in 2014, with increasing environmental impacts by this industry, mainly through CO2 emissions and consumption of non-removable raw materials. Several by-products have been used as raw materials or fuels to reduce environmental impacts. Basaltic waste collected by filters was employed as a mineral mixture to Portland cement and two fractions were tested. The compression strength of mortars was measured after 7 days and Scanning Electron Microscopy (SEM) and Electron Diffraction Scattering (EDS) were carried out on Portland cement paste with the basaltic residue. Gains in compression strength were observed for mixtures containing 2.5 wt.% of basaltic residue. Hydration products observed on surface of basaltic particles show the nucleation effect of mineral mixtures. Clinker substitution by mineral mixtures reduces CO2 emission per ton of Portland cement.


Introduction
Portland cement is widely used for building material and, according to Cembureau (2014), approximately 4.3 billion tons were processed in 2014.The 2014 Brazilian production reached 81 million tons of Portland cement.Several researches have been recently developed to reduce the environmental impacts of the cement industry, mainly by the co-processing of residues as raw materials (Schneider, Romer, & Bolio, 2011) or fuel (Cembereau, 2013).Currently, emission of particulated material has been restricted by environmental codes, resulting in residues collected by filters (Kim, Park, & Kim, 2013), which, in turn, are used as a mineral admixture to Portland cement (Hekal, Abo-El-Enein, El-Korashy, Megahed, & El-Sayed, 2013).However, several minerals, such as basalt and granite, do not have large scale industrial application and require environmental management.
Many studies have been developed for the proper disposal of these residues, such as raw material for clinker production (Andrade, 2010) or as mineral admixture to Portland cement (Uysal & Sumer, 2011).Hassan (2001) presents similar rates of compressive strength for clinkers obtained from basalt as raw material when compared to clinkers obtained from clay.Yen, Tsegn, and Lin (2011) published similar results for clinker produced from marble waste.Results published by Laibao, Zhang, Zhang, Zhiyoug, and Zhang (2013) have shown a loss of compressive strength for mixtures with basaltic waste as a mineral admixture (Figure 1).Unicik and Kmecova (2013) published similar results for mixtures containing 10, 20 and 30 wt.% of basaltic residue.Uysal and Yilmaz (2013) reported compression strength loss for all mineral admixtures when they compared mixtures containing 10, 20 and 30 wt.% of basalt, marble or calcium carbonate residues.Similar results were published by Vijayalakshimi, Sekar, and Ganeshm (2013) for mixtures containing 5, 10, 15 and 20 wt.% of granite waste.In the case of large amounts of mineral admixture, Jain (2012) presents a linear reduction in compression strength for mixtures containing 20, 40 and 60 wt.% of marble residue.Similar results were obtained by Vardhan, Goyal, Siddique, and Singh (2015) for formulations containing 10, 20, 30, 40, 50 wt.% of marble waste.In the case of mixtures with 34 wt.% of marble residue, Tennich, Kallel, and Ouezdoul (2015) presented a compression strength gain when compared to reference.Almeida, Branco, Brito, and Santos (2007) reported a gain on compression strength for mixtures containing 8 wt.% of marble residue for self-compact concretes with 0, 8, 15, 22, 27, 39, 56, 65 wt.% of marble waste.
According to Aictin (2000), ultrafine particles act as natural nucleation sites for the formation of calcium hydroxide (CH).They are developed as small Portlandite crystals, or calcium silicate hydrate and calcium aluminate hydrate (CSH/CAH).Mass loss at a temperature between 100 and 200 o C does not constitute a considerable difference for mixtures with 7.5 and 15 wt.% of granite residue, when compared with reference (Aliabdo, Elmoaty, Elmoaty and Auda (2014).The peak intensity of calcium hydroxide (CH) measured by X-ray diffraction does not present a considerable difference in spite of smaller amounts of clinker in mixtures containing the mineral admixtures (Laibao, Zhang, Zhang, Zhiyoug, & Zhang, 2013;Aliabdo et al., 2014).Current study evaluates a Coarse Fraction (< 200 micrometers) and a Fine Fraction (50 micrometers) of basaltic residue, both obtained by sedimentation, as a mineral admixture to Portland cement.

Materials
Basalt residue collected by filters was separated by sedimentation into two fractions: Coarse Fraction (CF) and Fine Fraction (FF).Portland cement CPV and natural sand were used in current study, following Associação Brasileira de Normas Técnicas (ABNT, 1991;2012), respectively.The chemical composition of basaltic fractions was determined by X-ray fluorescence, with P'ANalytical Axios Advanced X-ray spectrometer.The chemical composition of Portland cement CPV was provided by the manufacturer (Table 1).As may be seen in Figure 2, the particle size distribution of Coarse Fraction (CF), Fine Fraction (FF) and Portland cement (PC) was determined by laser granulometry with Malvern Metasizer 2000 granulometer.Figure 3 shows the diffractogram of Fine Fraction (FF).Data were measured with a Philips P'ANalytical X'Pert PRO MPD X-ray diffractometer (Cu 40 kV 30 mA Kα 2θ = 10 -70° 0.1° s -1 ). Figure 3

Methods
Table 2 shows a list of all studied mixtures.The mortar's compression strength followed ABNT (1997), using three 5 x 10 cm cylindrical specimens, employing a water: (cement-mineral admixture), ratio 0.48; and a (cement-mineral admixture): sand at a proportion of 1:3.After one day of initial curing, the specimens underwent submerged curing at room temperature (20°C).Following ABNT (1991), compression strength of Portland Cement CPV was measured after 1, 3, 7 and 28 days.For comparative analysis, compression strength was measured after 7 days.Mortar samples were ground and sifted in a 200-mesh sieve (0.075 mm) and calcined at 950ºC (American Society for Testing and Materials [ASTM], 2013).Water absorption of mortars was determined according to American Society for Testing and Materials (ASTM, 1972).The microstructural effect of basaltic powder was analyzed in pastes containing 15 wt.% of Fine Fraction (FF) with a Scanning Electron Microscope (SEM) Quanta 600 FEI-Philps.The paste samples were molded with the same water:(cement-mineral admixture) ratio, employing a silicone cylindrical mold, and subjected to submerged curing for 7 days at room temperature (20°C).Samples were dried and gold-coated.

Results and discussion
Figure 4 demonstrates the results of compression strength mortar samples.Reduction of compression strength occurs in mixtures containing Coarse Fraction (CF) due to increase in mineral admixture (Laibao et al., 2013;Unicik & Kmecova, 2013;Uysal & Yilmaz, 2013).In the case of samples containing 2.5 wt.% of Fine Fraction (FF), a gain in compression strength was observed and for mixtures with 5 wt.% of Fine Fraction (FF), a similar rate was obtained when compared to the reference mixture (Aruntas, Guru, Dayi, & Tekin, 2010).A subsequent reduction was verified for contents above 10 wt.% for a large quantity of Fine Fraction (FF).No considerable difference was reported with regard to compression strength for mixtures with large amounts of the two fractions.When water absorption of samples, displayed in Table 3, is taken into account, a constant trend in open porosity is given for the two fractions analyzed.According to Taylor (1990), loss of mass occurred up to 300 o C, which corresponded to the chemically bounded water from etringite (E), calcium silicate and aluminate hydrate silicate (CSH/CAH).Calcium hydroxide (CH) loses mass at temperatures ranging between 300 and 600 at 950 o C, mass loss represents calcium carbonate (CaCO 3 ) from the reaction of calcium hydroxide (CH) with CO 2 .Figure 5e shows a basaltic particle and hydration products such as calcium silicate hydrates (CSH) and calcium hydroxide (CH).Figure 5f reveals small quantities of calcium silicate hydrates (CSH) on the particles' surface, indicating nucleation effect.A point on the basaltic particle was analyzed with a back-scattered electron probe (EDS) to identify the semi-quantitative chemical composition.Figure 6 shows the obtained spectrum, highlighting the predominance of Si peak when compared to Ca, Mg, Na, K peaks, consistent with basalt chemical composition (Table 1).

Conclusion
The mechanical performance of Portland cement is directly affected by basalt residue.A positive effect was observed for contents varying between 2.5 and 5 wt.% of Fine Fraction, although a negative effect was identified on compression strength for larger amounts of mineral admixture.Consequently, the distribution of particle size directly affects the mechanical performance of the mixtures under analysis.
The nucleation effect was also identified for all studied mixtures; content of mineral admixture and the particle size distribution were two main aspects related to total hydration products.MEV analysis visualizes the nucleation effect which occurs on the surface of basaltic particles.The replacement of clinker by basalt waste contributes towards the reduction of emission of greenhouse gases.

Figure 1 .
Figure 1.Effect of mineral admixture on compression strength.

Figure 2 .
Figure 2. Particle size distribution of raw material.

Figure 4 .
Figure 4. Effect of basaltic powder on compression strength.

Table 1 .
Chemical composition of raw materials.