Scholarly article on topic 'Influence of Cement and Sand Type on the Strength Characteristics of Mortars with Various Contents of Green Binder'

Influence of Cement and Sand Type on the Strength Characteristics of Mortars with Various Contents of Green Binder Academic research paper on "Civil engineering"

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{"green binder" / "cement replacement" / "mechanical properties"}

Abstract of research paper on Civil engineering, author of scientific article — Ionut-Ovidiu Toma, George Taranu, Ana-Maria Toma, Mihai Budescu

Abstract The present paper brings its contribution to the investigation on the use of a new binder, in the form of anhydrous calcium sulphate, as partial replacement of the ordinary Portland cement in concrete. The eco-binder is obtained exclusively from industrial wastes and can be entirely recycled after its expiration date. The results obtained so far show a decrease in the flexural and compressive strengths of mortars with small replacing percentages of anhydrous calcium sulphate. However, the flexural strength increases tremendously for higher percentages of anhydrous calcium sulphate. Slight gains in the values of the compressive strength were also observed for the considered specimens.

Academic research paper on topic "Influence of Cement and Sand Type on the Strength Characteristics of Mortars with Various Contents of Green Binder"

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Procedía Engineering

ELSEVIER

Procedía En gineering2 1 (2011) 196 - 203

www.elsevier.com/locate/procedia

2011 International Conference on Green Buildings and Sustainable Cities

Influence of cement and sand type on the strength characteristics of mortars with various contents of green

binder

Ionut-Ovidiu Tomaa*, George Taranua, Ana-Maria Tomaa, Mihai Budescua

a "Gheorghe Asachi" Technical University of Iasi, Faculty of Civil Engineering and Building Services, 43rd Prof. D. Mangeron

Blvd., Iasi, 700050, Romania

The present paper brings its contribution to the investigation on the use of a new binder, in the form of anhydrous calcium sulphate, as partial replacement of the ordinary Portland cement in concrete. The eco-binder is obtained exclusively from industrial wastes and can be entirely recycled after its expiration date. The results obtained so far show a decrease in the flexural and compressive strengths of mortars with small replacing percentages of anhydrous calcium sulphate. However, the flexural strength increases tremendously for higher percentages of anhydrous calcium sulphate. Slight gains in the values of the compressive strength were also observed for the considered specimens.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of APAAS

Keywords: green binder; cement replacement; mechanical properties

1. Introduction

The production on cement alone has increased dramatically over the last century due to a continuous demand for concrete. According to a U.S. Geological Survey statistic report, the cement production increased, worldwide, from 62.4 million tons, in 1926, to 3.06 billion tons, in 2009. More than 50% of the reported increase took place over the last 12 years. Taking into account that the concrete industry is the largest consumer of natural resources in the world, one could only imagine the environmental burden the construction industry creates [1, 2]. Due to the increased awareness on the environmental impact of the construction industry [3, 4] extensive efforts have been put to reduce the CO2 emissions.

* Corresponding author. Tel.: +40-232-239213; fax: +40-232-239213. E-mail addresses: iotoma@ce.tuiasi.ro

Abstract

1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.11.2004

Concrete is the most widely used construction material. This is due mainly to its low maintenance costs. In spite of minor and temporary setbacks, e.g. freezing and thawing resistance, alkali-silica reaction, concrete is still the material of choice when it comes to severe exposure conditions. However, perhaps the biggest advantage of modern concrete is the possibility of including other industrial byproducts into the concrete mix [5]. This leads to the possibility of creating new, hybrid, materials with tailored mechanical properties to meet any possible requirements. Considerable research effort has been put to develop concretes with large volumes of fly ash [6, 7]. Ground granulated blast furnace slag has also found its use as partial replacement of Portland cement and also as aggregate [8]. The huge success silica fume has as pozzolan and filler material [9, 10] is another example of this great advantage of concrete.

Taking into account that demolition waste generates around 300 million tons of debris per year in the United States alone [5] it becomes clear that storing these solid wastes in landfills is no longer a viable option. Extensive research has been conducted in the field of using the solid wastes generated by the construction industry as recycled aggregates for concrete [11, 12].

The present paper brings its contribution to the investigation on the use of a new binder, in the form of anhydrous calcium sulphate, as partial or total replacement of the ordinary Portland cement in concrete. Nowadays there is still little research related to the total replacement of the ordinary Portland cement (OPC) by equivalent binders. The anhydrous calcium sulphate (ACS) based binder is obtained exclusively from industrial wastes and can be entirely recycled after its expiration date. Its production does not involve any CO2 emissions either.

The results presented herein are part of a larger research project related to the use of eco-materials for the structural rehabilitations of buildings located in seismic areas. The influence of the ACS on the mechanical properties of mortars with mineral matrix is investigated for different percentages of OPC replacement. The second parameter of the research was the maximum grain size of the sand part. The main focus was on the flexural strength and on the compressive strength. The mechanical characteristics were determined according to SR EN 196-1:2006 [13] provisions at different curing ages of the mortar specimens.

• Materials and Experimental Methodology

• Anhydrous Calcium Sulphate (Green-Binder)

• The anhydrous calcium sulphate was used as a replacement for the cement. The percentages used in this research were: 10%, 15% and 20%. Together with the cement, the ACS is used to obtain a more eco-friendly binder for mineral matrices. The anhydrous calcium sulphate, in the form of p anhydrite III' [14], was obtained from industrial wastes, most of them unrecyclable such as: phosphogypsum (industrial waste from the production of phosphoric acid, a key ingredient for fertilizers and detergents), flue gas desulphurization gypsum, FGD (industrial waste from coal fire power plants), lactogypsum (industrial waste from the production of lactic acid, used mainly in food preservatives), a.s.o.

• According to the invention patent [14], the production of ACS involves low temperatures and no CO2 emission at all. Moreover, it is entirely recyclable after its expiration date. The grain size ranges from 5 ^m to 100 ^m and the surface area is larger than 10 m2/g.

• Cement

• Two types of cement were used at this stage of the research. Type II cement, CEM II B-M 32.5R, is a high early strength cement produced according to SR EN 197-1:2002 code [15]. It is considered to be a composite cement with only 65-75% Portland cement and 25-35% ground granulated blast furnace slag (GGBS). According to the CEMBUREAU statistics [16], almost two thirds of the cement market in Europe corresponds to the use of CEM II cement. The other type of cement used in the experimental investigations was ordinary high early strength Portland cement, CEM I 42.5R, also produced according to [30].

Ionut-Chiidiu Torna et al./ProcediaEngmeermg 21(2011)196-203

• Sand

• The influence of the sand grain size was also considered as a parameter in the present research. Two sand types were taken into account with grain sizes between 0 - 0.3 mm and 0 - 1 mm. It has been shown that the sand grain size and type have an influence on the material structure of mortars [17, 18]. The findings are in accordance with previous research works related to the coarse aggregate size on the concrete behavior under uniaxial compression [19].

• In the present paper, the influence of the maximum sand grain size is investigated from the point of view of tensile and compressive strength of mortar prisms. The sand was used in its dry state for each mix proportion.

• Experimental Procedure

• The specimens were cast in standard size molds having the dimension 40 x 40 x 160 mm. After 24 hours the specimens were demolded and stored until the day of testing. The testing samples made only of ordinary Portland cement and sand were stored in water whereas the specimens made of Portland cement, calcium sulphate and sand were stored at room temperature.

• The specimens for each considered mix proportion were tested at the ages of 1, 2, 3, 7, 14, 21 and 28 days in order to determine the tensile strength and the compressive strength. The main parameters of the research were the type of cement, the sand type and the percentage of cement replacement by the calcium sulphate. The mix proportions made with CEM I 42.5R type of cement and considered at this stage of the research are summarized in Table 1. The same mix proportions were used for the CEM II B-M 32.5R type of cement but only the case of maximum sand grain size of 1.0 mm was considered. The water to binder ratio was kept constant for all mix proportions.

• The sand is considered to fill 50% of the total volume and the remaining percentage is made by the binder. The binder consists either of OPC or a mixture of OPC and ACS. Each mix proportion was named in terms of cement type, percentage ACS used as well as the maximum grain size of sand. Hence, "C" stands for cement, followed by the type of cement, either "I" or "II". The designation continues with a number showing the percentage of ACS considered as replacement for OPC and it ends with the specification of the maximum grain size of sand, either "0.3" or "1.0".

• The tensile strength of the mineral matrix was determined by means of three point bending test, Fig. 1., with a constant loading rate of 0.05 kN/s. Three prismatic specimens were used for each determination of the tensile strength. The compressive strength was determined on the two resulting halves of the prism, Fig. 2. Prior to that, the two halves were examined for the presence of cracks that might have been generated during the three point bending test. The loading rate was 2.4 kN/s for the uniaxial compression test.

Table 1. Mix proportions considered in the research (designation only for CEM I)

Specimen Designation Binder OPC (CEM I / II) ACS Sand Water / Binder

% % % %

CI-0-1.0 50 0

CI-10-1.0 40 10 50 40

CI-15-1.0 35 15

CI-20-1.0 30 20

Fig. 1. Three-point bending test of mortar prism Fig. 2. Uniaxial compression test on a half prism

Results and Discussions

• The results are discussed in terms of tensile strength and compressive strength experimentally determined at the ages of 1, 2, 3, 7, 14, 21 and 28 days. The main parameters in this study are the type of Portland cement, the maximum grain size of sand and the percentage of ACS used in the mix proportion. A total number of 12 mix proportions were considered leading to 144 specimens cast and tested.

• Percentage of cement replacement

• Figures 3 shows the variation of the tensile strength for the specimens made with CEM II cement and maximum sand grain size of 1.0 mm. High values of the tensile strength can be observed at the age of 24 hours for all testing samples. There is an initial scatter in the values of the tensile strength, between 3.04 MPa and 4.11 MPa at the age of 24 hours. However, at the age of 7 days, the measured values of the tensile strength for each specimen are close to one another, despite the percentage of ACS used to replace the Portland cement. After the age of 7 days, the CII-15-1.0 case shows a rapid increase in the value of the tensile strength up to 8.76 MPa and stays relatively constant until the end of the considered time interval. The reference sample shows a steady increase in the value of the tensile strength over the first three weeks and a steeper change during the last week of the time interval. At the age of 28 days, the value of the tensile strength for the reference sample comes very close to the value of 10.07 MPa recorded for the CII-15-1.0 case. The CII-10-1.0 and CII-20-1.0 case show similar behavior, reaching a maximum value of 8.15 MPa for the tensile strength at 28 days.

• Figure 4 presents the variation of the compressive strength obtained for the mix proportions made with CEM II cement. There is a sharp increase in the values of the compressive strength during the first 3 days. The reference sample continues to gain strength until the age of 28 days. The specimens made with difference percentages of green binder shown almost constant values of the compressive strength from the age of 7 days until the end of the considered time interval. All specimens made with green binder exhibited lower compressive strength values compared to the reference sample but well above the required values for normal class civil engineering structures. As with the tensile strength, the CII-15-1.0 case showed higher values, by as much as 17%, compared to the other specimens having ACS in their mix proportions.

• Based on the results obtained so far it can be concluded that the use of ACS as partial replacement for Portland cement is encouraging. The results are even more promising when considered from the point of view of the ratio between the tensile and compressive strength. While the reference specimen had a ratio of 1/7, all mix proportions with partial replacement of Portland cement had a ratio of 1/4. This

Ionut-Chiidiu Toma et al./ProcediaEngmeermg 21(2011)196-203

could lead to a more rational design of civil engineering structures.

• Cement type

• The values of the tensile strength at each considered time stamp are presented in Fig. 5 for the specimens made with CEM I cement and a maximum sand grain size of 1.0 mm. It can be observed that there is a big scattering of the results for the entire duration of the time interval. The reference sample shows a rather constant evolution of the tensile strength, reaching a value of 6.76 MPa at the age of 28 days. From the age of 3 days, the CI-20-1.0 case exhibits a sudden increase in the value of the tensile strength and the trend remains the same until the age of 14 days. It then slightly decreases until the end of the time interval when it reaches a value of 9.38 MPa. This is 15% higher than the CII-20-1.0 case. This is the only instant when the specimens made with CEM I cement show higher values

Fig. 3. Tensile strength of the CII-1.0 case Fig. 4. Compressive strength of the CII-1.0 case

• It can be concluded that the green binder reacts better with the CEM II cement, yielding higher values of the tensile strength, by as much as 30%, and less scattering of the results.

• Figure 6 shows the variation of the compressive strength for the specimens made with CEM I cement and sand having a maximum grain size of 1.0 mm. There is less scattering in the obtained values for the specimens made with different percentages of green binder. The compressive strength is slightly higher at the age of 28 days compared with the samples made with CEM II cement. The obtained values are 11% higher than the previous case.

• The ratio between the tensile and compressive strength for the specimens made with difference percentages of ACS is between 1/6 and 1/4, slightly less than in the case of CEM II samples. It can be therefore concluded that the type of cement used together with the green binder plays an important role in the obtained results.

• Maximum grain size of sand

• The same mix proportions made with CEM I cement were considered again but the sand was replaced with finer grain sand having a maximum grain diameter of 0.3 mm.

• Figure 7 shows the variation of the tensile strength for the specimens made with CEM I cement and with sand having a maximum grain diameter of 0.3 mm. Similar scattering can be observed in the

values of the tensile strength as with the specimens made with the same cement but coarser sand. CI-15-0.3 and CI-20-0.3 cases show the highest values of the tensile strength. The values are slightly higher compared with the samples made with coarser sand. The difference is between 1% and 11%. The tensile strength of the reference samples are almost the same in both cases. The overall values are still lower compared to the CEM II specimens.

• The evolution of the compressive strength for the specimens made with CEM I cement and finer sand is presented in Fig. 8. The behavior is similar to the samples made with coarser sand and the same cement type. However, as with the case of tensile strength, the values are 7.5% higher. This difference was recorded only for the specimens with partial replacement of the Portland cement.

• The ratio between the tensile and the compressive strength varies within the same range with the samples made with coarser sand. Based on the obtained results, it can be concluded that the maximum grain size of the sand influences the values of both the tensile and the compressive strength but not by a significant amount. Higher values were expected for the mechanical properties of specimens made with finer sand as it fills the voids better and helps obtaining a more compact mortar. Similar results were also reported in literature for mortars [20].

•—CI-0-1.0 ■—CI-10-1.0 ♦—CI-15-1.0 0—CI-20-1.0

12 16 Age [days]

12 16 Age [days]

Fig. 5 Tensile strength of the CI-1.0 case

Fig. 6 Compressive strength of the CI-1.0 case

Ioout-OvidiuTorrui et al./ProcediaEngineering21 (2011) 196-203

0 4 8 12 16

Age [days]

Fig. 7. Tensile strength of the CI-0.3 case

2. Conclusions

I I ! •— CI-0-0.3 ■— CI-10-0.3 ♦—CI-15-0.3 0—CI-20-0.3

T-1-1-!-1-T

i_I_I_I_i_L

0 4 8 12 16 20

Age [days]

Fig. 8. Compressive strength of the CI-0.3 case

The present paper brings its contribution to the investigation on the use of a new binder, in the form of anhydrous calcium sulphate, as partial or total replacement of the ordinary Portland cement in concrete. Taking into account that it is made from industrial wastes, most of them unrecyclable, and that its production does not involve CO2 emissions, it comes as a prime candidate for solving the problem of land fills and the reductions of CO2 emissions from cement plants.

The experimental investigations show that the use of ACS lead to higher values of the tensile strength of mortars compared to the values obtained on reference samples made only with Portland cement and sand. This observation is valid for percentages of ACS between 15 - 20% of the total volume and does not depend on the type of cement or on the maximum grain size of sand. This strongly recommends the ACS as a viable solution for the replacement of Portland cement in civil engineering practice. However, there is a need for further investigations in this field, mainly related to the expansive behavior of the mineral matrix made with different percentages of anhydrous calcium sulphate.

The use of CEM II composite cement yields better results in terms of the tensile strength and scattering of the obtained values. On the other hand, the use of CEM I cement leads to higher values of the compressive strength by as much as 11 %.

The maximum grain diameter of the sand seems to have a larger influence on the tensile strength, 11%, than on the values of the compressive strength, 7.5%. In both cases, the higher values are obtained for the specimens made with finer sand.

Acknowledgements

This paper was supported by the project "Develop and support multidisciplinary postdoctoral programs in primordial technical areas of national strategy of the research - development - innovation" 4D-POSTDOC, contract nr. P0SDRU/89/1.5/S/52603, project co-funded from European Social Fund

through Sectorial Operational Program Human Resources 2007-2013.

The authors would also like to thank Carpatcement Holding S.A. for supplying the CEM I type of cement used in this research. Their contribution is greatly appreciated.

References

[1] Arikan K., Feasibility analysis of manufacturing high-performance-ecological-cement in Turkey. Eeildiuo mud Environment 2004; 39(9): 1125-1130.

[2] Blom I., Itard L. and Meijer A., Environmental impact of dwellings in use: maintenance and façade components. Eeildiuo mud Environment 2010;45(11): 2526-2538.

[3] Rehan R. and Nehdi M., Carbon dioxide emissions and climate change: policy implications for the cement industry. Environmental Science andPolicy 2005; 8(2): 105-114.

[4] Spaargaren G. and Mol A.P.J., Greening global consumption: redefining politics and authority. Gleb/l Environmental Change 2008; 18(3): 350-359.

[5] Meyer C. The greening of the concrete industry. Cement and Concrete Cempesites 2009; 39(8): 601-605.

[6] Aggarwal V., Gupta S.M. and Sachdeva S.N., Concrete durability through high volume fly ash concrete - a literature review. I2teg2/tie2/l Journal of Engineering Science and Technology 2010; 2(9): 4473-4477.

[7] Karahan O. and Ati§ C.D. The durability properties of polypropylene fiber reinforced fly ash concrete. Materials and Design 2011;32(2): 1044-1049.

[8] Mozaffari E., Kinuthia J.M., Bai J. and Wild S. An investigation into the strength development of wastepaper sludge ash blended with ground granulated blast furnace slag. Cement and Concrete Research 2009; 39(10): 942-947.

[9] Gonzales-Fonteboa B. and Martinez-Abella F, Concretes with aggregates from demolition waste and silica fume. Materials and mechanical properties, Eeilding and Environment 2008; 43(4): 429-437.

[10] Ivorra S., Garces P., Catala G., Andion L.G. and Zornoza E., Effect of silica fume particle size on mechanical properties of short carbon fiber reinforced concrete, Materials and Design 2010;31(3): 1553-1558.

[11] Etxeberria M., Vazquez E., Mari A. and Barra M., Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete.Cement and Concrete Research 2007;37(5): 735-742.

[12] Berndt M.L., Properties of sustainable concrete containing fly ash, slag and recycled concrete aggregate, Construction and Building Materials 2009; 23(7): 2606-2613.

[13] Methods for cement testing. Part I: The determination of mechanical properties, SR EN 196-1:2006 (in Romanian).

[14] Process for the Industrial Manufacture onf Compositions Eased on Onhydroes C/lciem Selph/te in the E-Onhydrite III' Form, and Corresponding Compositions andEinders, WO 2010/003827 A1, January, 2010 (in French).

[15] Cement. Part I: Composition, specifications and conformity criteria of cement, SR EN 197-1:2002 (in Romanian).

[16] Cembureau. World Statistic Review 1996-2006. CEMBUREAU (European Cement Association); 2008.

[17] Diamond S. and Kjellsen K.O., Scanning electron microscopic investigations of fresh mortars: Well-defined water-filled layers adjacent to sand grains, Cement and Concrete Research 2008; 38(4): 530-537.

[18] Cortes D.D., Kim H.-K., Palomino A.M. and Santamaria J.C., Rheological and mechanical properties of mortars prepared with natural and manufactured sands. Cement and Concrete Research 2008; 38(10): 1142-1147.

[19] Akcaoglu T., Tokyay M. and Celik T., Effect of coarse aggregate size and matrix quality on ITZ and failure behavior of concrete under uniaxial compression. Cement and Concrete Composites 2004; 26(6): 633-638.

[20] Stefanidou M. and Papayianni I.The role of aggregates on the structure and properties of lime mortars. Cement and Concrete Composites 2005; 27(9-10): 914-919.