Scholarly article on topic 'The Effect of Basalt Powder on the Properties of Cement Composites'

The Effect of Basalt Powder on the Properties of Cement Composites Academic research paper on "Materials engineering"

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Procedia Engineering
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{"basalt powder" / rheology / concrete / polycarboxylate}

Abstract of research paper on Materials engineering, author of scientific article — Stanislav Unčík, Veronika Kmecová

Abstract The paper deals with the effect of basalt powder on the rheological properties of fresh cement mortars and physical properties of hardened mortars. The cement mortar was modified by basalt powder in amount 10, 20 and 30% by weight of cement (replacement of cement). The consistence of fresh mortars should have the quality of self-compacting material. The impact of basalt powder on the initial consistency and on the loss of workability was studied. The effect of basalt powder on the shrinkage and compressive strength was also investigated. The results obtained show that the basaltic powder has a positive effect on the consistency of fresh cement composites and the strength of the hardened composite.

Academic research paper on topic "The Effect of Basalt Powder on the Properties of Cement Composites"

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Procedía Engineering

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Procedía Engineering 65 (2013) 51 - 56

www.elsevier.com/locate/procedia

Concrete and Concrete Structures 2013 Conference

The Effect ofBasalt Powder on the Properties of Cement

Composites

Stanislav Uncika*, Veronika Kmecováa

3Faculty of Civil Engineering STU, Radlinskeho 11, 813 68 Bratislava, Slovak Republic

Abstract

The paper deals with the effect of basalt powder on the rheological properties of fresh cement mortars and physical properties of hardened mortars. The cement mortar was modified by basalt powder in amount 10, 20 and 30 % by weight of cement (replacement of cement). The consistence of fresh mortars should have the quality of self-compacting material. The impact of basalt powder on the initial consistency and on the loss of workability was studied. The effect of basalt powder on the shrinkage and compressive strength was also investigated. The results obtained show that the basaltic powder has a positive effect on the consistency of fresh cement composites and the strength of the hardened composite.

© 2013The Authors.Publishedby ElsevierLtd.

Selectionandpeer-review underresponsibilityof University ofZilina,Faculty of CivilEngineering, Department of Structures andBridges

Keywords: basalt powder, rheology, concrete, polycarboxylate;

1. Introduction

Production of Self-Compacting Concrete (SCC) is a relatively new technology. SCC is recently one of the most evolving materials in the construction industry. It is a material that does not requires the use of vibrational energy to achieve a compact structure of concrete. SCC has good deformation ability, high resistance to segregation and the ability to fill heavily reinforced formwork without aggregate blocking.

A new generation of chemical and mineralogical admixtures added to SCC improves cohesion and resistance to segregation. Hardened SCC is dense, homogeneous and has greater durability than traditional vibrated concrete [1,2]. Key steps in the design of SCC include selection of appropriate materials and designing appropriate procedures for concrete placement in order to achieve adequate properties of fresh concrete after its placing.

Mineral admixtures generally improve rheological properties of fresh concrete. They improve cohesion and reduce the tendency for segregation. These materials may also reduce the hydration heat and improve long-term

*Tel.: +421 2 5927 4686. E-mail address: Stanislav.uncik@stuba.sk

1877-7058 © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of University of Zilina, Faculty of Civil Engineering, Department of Structures and Bridges doi:10.1016/j.proeng.2013.09.010

properties of hardened concrete. Use of mineral admixtures in SCC enables reduction in amount of superplasticizer necessary to reach the desired consistency [1,2] , [5].

Commonly used mineral admixtures are usually byproducts of industrial production, or waste materials such as silica fume, blast furnace slag, limestone powder, etc. Basalt powder is a by-product of stone crushing in basalt quarries. High amounts of gathered powders are a big problem from the point of view of the disposal, environmental pollution and health risks. The use of mineral dusts as admixtures in concrete can contribute to solving these problems.

This paper presents the results of a study on effect of basalt powder on the properties of fresh and hardened cement mortars.

2. Experimental section

2.1 Materials

The effect of basalt powder in combination with the superplasticizer on properties of cement mortars was studied on cement mortars prepared from Portland cement CEMI 42,5 R. Composition and basic properties of the cement are shown in Table 1.

Natural river aggregates (location Okoc), from sediments of river Small Danube was used for the production of cement mortar. It was composed of three fractions 0/1 0/4 and 2/4. Mixing ratio was as follows: 0/1 = 15%, 0/4 = 55%, 2/4 = 30%. Grading of the aggregate fractions and optimal sieving curve are illustrated in Figure 1.

Superplasticizer (SP) based on polycarboxylate Berament HT 5221 was used for the production of cement mortar. Basic properties of the admixture are shown in Table 2.

As an additive in cement mortar was used basalt powder (BP). Its chemical composition and fineness are shown in Table 3.

Drinking water from a public water supply system was used for the production of cement mortar.

Table 1. Composition and physical properties of cement

Chemical composition Mineralogical composition Physical properties

CaO 62.88 % Alite 56.50 % Standard consistency 29.6 %

Si02 20.50 % Belite 13.71 % Initial setting 150 min.

ai2o3 5.76 % C3A total 10.38 % Final setting 190 min.

Fe203 2.72 % C3A cubic 2.62 % Soundness 5.0 mm

MgO 1.32% C3A ortho 7.76 % Compressive strength after 2 days 30.0 MPa

Na20 0.27 % Ferrite 8.52 % Compressive strength after 28 days 53.6 MPa

k2o 1.14% Anhydrite 3.72%

so3 2.92 % so3 3.56 % residue on sieve 0.2 mm 0.0 %

MnO 0.055 % MgO 2.61 % Fineness: residue onsieve 0.09 mm 0.3 %

Ti02 0.155 % Portlandite 1.80 % residue on sieve 0.063 mm 0.8 %

p2o5 0.146 % Hemihydrate 1.70%

CI 0.150 % Periclase 1.26 %

Table 2. Physical properties of superplasticizer Berament HT 5221

Appearance Homogeneous light brown solution

Density 1.063 g.ml"1

Dry matter content 28.1 %

pH at 20 °C 4.51

• Fraction 0/4 »• Fraction 2/4 » Fraction 0/1 ™ Optimal mixture

Table 3. Chemical composition and fineness of basalt powder Chemical composition Si02 44.59 % A1203 15.05 % CaO 10.89 % Fe203 8.87 % MnO 0.26 % P205 0.6 % SQ3_0.02 %

Residues on sieve

0,063 mm 3.45 %

0,09 mm 1.55 %

0,2 mm 0.30%

2.2Experimental methods

The composition of the reference mortar without chemical and mineralogical admixtures is based on a modified standard mortar according to EN 196-1 [3]. It contained 450 g of cement, 1350 g of aggregate and 225 g of water. The amount of water was reduced on value 202.5 g (W/C = 0.45). This reference mortar was further modified by addition of superplasticizer and basalt powder (BP). The doses of superplasticizer were 0.5, 0.75, 1.0, 1.25 and 1.5 % by weight of cement. BP was dosed in amount 10, 20 and 30 % as a partial replacement of cement.

Amount of mixing water was reduced with the water contained in plasticizers in all mixtures to keep to the water-cement ratio at 0.45.

Cement mortars were mixed in a standard laboratory mixer according to EN 196-1 [3]. Immediately after mixing the consistency of fresh mortar was determined by using the Haegermann flow table (without use of lifting and dropping of flow table plate).

Cylindrical samples with diameter and height of 30 mm were prepared from the cement mortar for testing the compressive strength. For shrinkage testing the prisms with size of 40 x 40 x 160 mm were prepared. Test prisms were fitted with glass contacts at their ends.

Cement mortars in moulds were compacted adequately to their consistency. Test samples were cured for 24 h in a humid environment and further in water.

Compressive strength tests were determined using compression testing machine.

Shrinkage of mortars was determined by shrinkage measuring device by measuring the differences in length between mortars samples and metal etalon.

3. Results and discussion

Results of tests that were focused on the rheological properties of fresh cement mortars are shown in Fig. 2.

Sieve sizes [mm]

Fig. 1. Grading curves of aggregate used

Na20 MgO K20 Ti02

0.02 % 4.11 % 4.31 % 1.39% 1.03 % 8.84 %

The initial consistency of fresh mortar (Fig. 2. (a)) was positively affected by the addition of SP and BP. With increasing dose of superplasticizer the consistency of mortars without basalt powder gradually improved up to dose 1.25 %. At the dose 1.5 % there was observed mild segregation of mortar and separation of mixing water and also a reduced flow diameter of mortar. Mortar modified by superplasticizer in a dose of 0.75 % has begun to show signs of thixotropy and selfcompactability. These tendencies increased with increasing dose of SP.

Partial replacement of cement by BP in the cement mortar without SP has not improved the consistency (flow diameter) but at the small replacement (10 %) the mortar had better workability (preparation of samples was easier). Increase in BP content (20 and 30 %) led to a slight deterioration of workability.

The replacement of cement by BP in plasticized mortars led to a significant improvement in workability of fresh mortars. The flow diameter increased with increasing of proportion of BP to dose of supeplasticizer 0.75 %. At higher amount of plasticizer the flow diameter slightly decreased with increasing of BP portion, but it was still higher than in the case of cement mortars without BP (at the same dose of superplasticizer). Decrease in flow diameter can be explained by segregation and bleeding of mortars, which occurred at higher dose of superplasticizer and BP. During the test of consistency the mortars with higher tendency to segregation formed a thicker layer in the center of the circle (due to selfcompaction) while released water and fine particles were deployed around the perimeter. Therefore the flow diameter of these mortars was smaller than that of more homogenous mortars, despite the fact that these mortars were more fluid.

Based on results we can conclude that the basalt powder had additional plasticizing properties, greatly improved the consistency of the mortar, its cohesion and selfcompaction (at optimum dose).

□ 0%BP

□ 10 % BP

■ 20 %BP

■ 30 %BP

0,5 0,75 1 Dose of superplasticizer [%]

0%BP ■20% BP

60 90 Time [min]

■ 10% BP

■ 30% BP

Fig. 2. (a) Initial flow diameter of tested cement mortars (hatched bars represent mortars where segregation has occurred), (b) Workability loss of

cement mortars (dose of SP 1 %)

Fig. 2. (b) documents the change in workability of plasticized mortar with BP tested without dropping. Consistency of cement mortars continually decreased with time. Segregation of mortar resulted in a worsening of consistency at higher doses of BP and also caused a more rapid loss of workability.

One day and 28-day strength of mortars are given in Fig. 3. The replacement of cement by basalt powder led to decreasing of compressive strength of mortars. The loss of strength increased with content of BP in mortars. A significant decrease was shown in one-day strength while the decrease of 28-days strength was relatively slight. The loss of compressive strength is in conformity with expectation because the increasing proportion of BP in mortars means lower content of cement.

Smaller differences in strength after 28 days of hardening as is shown in Fig. 3 mean that mineral admixture used contributes to the development of strength. A similar trend has also been published by Uysal Yilmaz and Sumer [1,2].

The effect of various dosage of superplasticizer on the mortar strength was not very strong. Compressive strength of mortars without BP slightly increased with increasing dose of SP up to a dose of 1% and then began to decrease.

With the increased proportion of BP and dose of SP the strength of mortars decreased. This tendency was stronger at 1-day compressive strength. These results were obtained at constant water to cement ratio.

Decrease in strength of mortars with high doses of chemical and mineralogical admixtures was significantly affected by the segregation of the mortars, that led to their non-homogenous structure and consequently to a reduction in strength.

0,25 0,5 0,75 1 Dose of superplasticizer [%]

Dose of superplasticizer [%]

Figure 3. (a) 1- day compressive strength,(b) 28 - days compressive strength

The results of the shrinkage of cement mortars are given in Fig. 4.. Fig. 4. (a) shows the results of shrinkage tests performed on plasticized mortars. The greatest shrinkage after 56 days was found on mortar without superplasticizer. The shrinkage decreased with increasing dose of superplasticizer used.

Replacement of part of cement by basalt powder led to an increase in shrinkage (Fig. 4 (b)). The shrinkage of the mortars slightly increased with the basalt powder content with the exception of the mortar with BP content 30 %. Shrinkage of this mortar was smaller than the others with lower proportion of BP. This can be explained by the strong segregation of the mortar resulting probably in a smaller proportion of hardened cement paste in the mortar. Shrinkage of mortars well correlated with mass loss of cement mortars.

Figure 4. (a) Shrinkage of cement mortars without basalt powder, (b) Shrinkage of cement mortars at the dose of superplasticizer 1 %

4. Conclusions

The obtained results confirmed high effectiveness of used polycarboxylate superplasticizer. Use of this superplasticizer at dose equal or higher than 1 % by weight of cement resulted in obtaining mortars with self-compacting properties.

Replacement of part of cement by basalt powder in plasticized mortars resulted in significant improvement of their consistency.

At higher doses of the superplasticizer and the mineral additives the segregation of cement mortars occurred. The results demonstrate the positive effect of the superplasticizer used and also basalt powder on the strength of hardened mortars.

Replacement of cement by basalt powder led to a slight increase in shrinkage of cement mortars and also a slight increase in mass loss during curing in laboratory environment.

Based on the results presented we can assume that the basalt powder can be used in production of concrete to improve its properties. Use of this material also can reduce the environmental impacts connected with the extraction of basalt.

References

[1] M. Uysal, K. Yilmaz, Effect of mineral admixtures on properties of self-compacting concrete. Cement and Concrete Composites 33 (2011) 771-776.

[2] M. Uysal, M. Sumer, Performance of self-compacting concrete containing different mineral admixtures. Construction and Building Materials 25 (2011)4112-4120.

[3] STN EN 196 - 1 Methods of testing cement - Part 1: Determination of strength (1997).

[4] STN EN 12350 - 5 Testing fresh concrete - Part 5: Flow table test (2010).

[5] 1. Bekir Top9U, T. Bilir, T. Uygunoglu, Effect of waste marble dust content as filler on properties of self-compacting concrete. Construction and Building Materials 23 (2009) 1947-1953.

[6] STN EN 206 - 1/ NA Concrete - Part 1: Specification, performance, production and conformity. National annex SR (2009).