Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2024.47.0066 Acta Polytechnica CTU Proceedings 47:66–70, 2024 © 2024 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague PRODUCTION OF CONCRETE PAVEMENTS USING MIXED CEMENTS Jan Klobása∗, Rudolf Hela Brno University of Technology, Faculty of Civil Engineering, Institute of Technology of Building Materials and Components, Veveří 331/95, 602 00 Brno, Czech Republic ∗ corresponding author: 197260@vutbr.cz Abstract. Currently, great importance is attached to the reduction of emissions in industrial production, especially in the production of cement, when it is indicated that during production 1 ton of cement produces approximately 0.6 ton of CO2. Reducing emissions is possible thanks to secondary raw materials, which are produced in large quantities in the Czech Republic volumes for which a suitable use is sought. Some secondary raw materials are suitable for use in concrete mixes, which are used to improve the rheology of the fresh concrete mixture as well as the properties hardened concrete. Currently, there is an effort to eliminate the production of cement, to which its partial replacement by admixtures could also contribute. Therefore it is necessary determine the optimal admixture that could be used to replace part of the cement in concrete mix. A large consumer of concrete mixes are transport structures, where it is possible for some of the cement used to be replaced by an admixture. Keywords: Cement, concrete pavemets, admixtures, durability, carbon footprint. 1. Introduction Concrete is mainly used in buildings and infrastructure around the world, where it is mainly produced using or- dinary portland cement (OPC) as a binder. In recent years, annual world cement production has increased from 1.0 billion tons to approximately 1.7 billion tons, which is enough to produce 1 m3 of concrete per per- son. As a result, the cement industry is generally considered to be a high growth industry. However, since the end of the 19th century, industry has been struggling with the need to reduce the burden on the environment, including carbon dioxide (CO2) emis- sions. Some estimates suggest that the amount of CO2 emissions from global OPC production may be as high as 7 % of total global CO2 emissions. In addition, the production of OPC is associated with serious environ- mental side effects, such as environmental pollution caused by dust and the enormous energy consumption required by the plasticity temperature above 1 300° C. For these reasons, the cement industry has been chal- lenged in the last 10 years to effectively reduce and control CO2 emissions [1–3]. Four alternative technologies to reduce CO2 emis- sions in the cement industry were commonly discussed; 1) changing the fuel to a fuel with a lower carbon con- tent, for example from coal to natural gas during the calcination of limestone; 2) adding a chemical absorption process to capture CO2 3) changing the clinker production process with efficient grinding and converting from a wet to dry process and 4) adding large volumes of supplementary cementitious materi- als (SCM) such as ground granulated blast furnace slag (GGBS), fly ash (FA) and/or silica fume (SF). Of these four technologies, the use of cement mixed with admixtures is the most practical and economical method that can be directly applied in the field of ready-mixed concrete. In addition, the use of GGBS or FA can provide additional environmental benefits, including conservation of natural resources and recy- cling of industrial by-products. Research has shown that the addition of additives is capable of reducing CO2 emissions by 22 %. They also pointed out that the greenhouse gas impact calculated from blended cement is reduced by up to approximately 22 % com- pared to traditional OPC [2, 4]. Concrete pavements are intended for very high traf- fic loads and as such are preferably used for the con- struction of airport runways, expressways or highways. Concrete for the production of these structures must meet the requirements for workability, mechanical resistance, resistance to climatic influences, anti-slip properties and must be resistant to the action of chem- ical de-icing agents, which are used in the maintenance of such surfaces in winter [5]. The steady increase in heavy freight traffic not only puts a strain on highways, but also on other pub- lic transport areas. Choosing the right technology at the right place is a difficult task for every road construction administration. At the same time, the requirements for durability and sustainability are in the center of attention. Therefore, decisions are being made more and more often about the construction of cement-concrete covers on traffic areas. In addi- tion to this, mixing cement with these raw materials can improve the long-term mechanical properties and durability of concrete and thereby extend the life of concrete structures [2–5]. 66 https://doi.org/10.14311/APP.2024.47.0066 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 47/2024 Production of concrete pavements using mixed cements Recipe CEM I CEM II/A-S CEM III/A CEM II/C-M CEM II/A-LL CEM II/B-M Raw Material 42.5 R (sc) 42.5 R 42.5 N (S-LL) 42.5 N 42.5 R (S-LL) 42.5 N [kg m−3] Mokrá Mokrá Hranice Hranice Radotín Radotín CEM 360 360 360 360 360 360 DTK 0/4 Tovačov 537 537 537 537 537 537 HDK 4/8 Rosice 181 181 181 181 181 181 HDK 8/16 Rosice 544 544 544 544 544 544 HDK 16/32 Rosice 544 544 544 544 544 544 Voda 165 165 185 175 170 182 Muraplast FK 19 1.8 1.8 1.8 1.8 1.8 1.8 Centrament Air 202 0.13 0.08 0.07 0.07 0.09 0.08 Table 1. Composition of concrete recipes. 2. Aims The aim of the article is the experimental verification of new types of cements and concrete mixes for cement- concrete road pavements with a significantly reduced carbon footprint and increased durability. The article is aimed at use in the field of transport constructions with a focus on the use of suitable mixed cements, reducing the formation of greenhouse gases to increase the service life of concrete pavements, extend the time for repairs and reduce the total costs for the construction and operation of the highway network in the Czech Republic. The main goal will be to assess the applicability of mixed cements for the production of cement-concrete covers due to the reduction of environmental impacts on our environment while achieving the required dura- bility, especially the XF4 environment. 3. Methodology This work deals with the lower layer of cement- concrete cover. The work was divided into 2 main stages. For the first stage, concretes with mixed ce- ments were designed and produced. In the last stage, the achieved results were processed and compared based on the results of physical and mechanical prop- erties with individual types of cement. 4. Used raw materials In the experimental part, 6 concrete mixtures were produced, differing from each other only in the ce- ment used. Two cements were used from the Mokrá cement plant, Portland cement CEM I 42.5 R (sc) and Portland mixed CEM II/A-S 42.5 R. Cements CEM II/A-LL 42.5 R and CEM II/B-M (S-LL) 42.5 N were used from the Radotín plant. And cements CEM III/A 42.5 N and CEM II/C-M(S-LL) 42.5 N from the Hranice cement plant. Four types of ag- gregates from two areas were used for production. The washed mined aggregate in fraction 0/4 was from the Tovačov locality and the coarse crushed aggregate in fractions 4/8, 8/16 and 16/32 from the Rosice lo- cality. Both the plasticizing additive Muraplast FK 19 and the aerating additive Centrament AIR 202 conc. were used from MC Bauchemie. The composition of the individual mixes produced is shown in Table 1. 5. Experiment When designing and mixing individual recipes, the goal was to achieve a consistency of fresh concrete mix- ture with a cone settlement in the range of 40–60 mm. During the mixing of the concrete mixture, the amount of water and plasticizer was adjusted due to the differ- ent compositions of the cements in order to achieve the desired consistency of the concrete. Furthermore, the air content was measured on the fresh concrete. A dif- ferent amount of aeration admixture was added to each mix to achieve an optimum fresh concrete air content of 6.5 %. Subsequently, the bulk density of the fresh concrete was determined according to ČSN EN 12350- 6, which ranged from 2 260 to 2 300 kg m−3. From each recipe, test bodies were produced (cube with an edge of 150 mm, beam 100 × 100 × 400) on which the physical and mechanical properties were determined. At the age of 2, 7, 28 and 90 days, the volumetric weight of the hardened concrete was tested accord- ing to ČSN EN 12 390-7 and the compressive strength according to ČSN EN 12 390-3 [6–8]. It follows from the measured results, see Figure 1 that the replacement of cement with admixtures signif- icantly negatively affects the short-term compressive strengths of concrete. As expected, the highest com- pressive strength after 2 days of maturation is achieved by road Portland cement, which contains the highest percentage of clinker. The higher the replacement of cement with admixtures, the lower the strengths. The lowest compressive strength value after 2 days was evaluated for CEM III/A from Hranice. The most significant increase in strength between 28 and 90 days is for the test samples that contain the active ingredi- ent. This difference may be caused by the pozzolanic activity, which becomes apparent after a longer period than 28 days. The highest compressive strength of all concretes was achieved after 60 days of curing. Con- crete with the used cement CEM II/A-S 42.5 R Mokrá achieves the highest compressive strength. As the age of the samples increased, the difference in strength values disappeared. 67 Jan Klobása, Rudolf Hela Acta Polytechnica CTU Proceedings Recipe Weight Flexural tensile Flexural tensile Degree of change strength ref strength frozen frost resistence [%] [MPa] [MPa] [%] CEM I 42.5 R (sc) Mokrá -0.17 5.9 6.3 106 CEM II/A-S 42.5 R Mokrá -0.28 5.4 5.8 108 CEM III/A 42.5 N Hranice -0.45 4.9 3.9 80 CEM II/C-M (S-LL) 42.5 N Hranice -0.36 5.1 4 78 CEM II/A-LL 42.5 R Radotín -0.88 4.8 4.3 89 CEM II/B-M (S-LL ) 42.5 N Radotín -0.66 5.3 5.2 96 Table 2. Evaluation of the frost resistance test. Figure 1. Strength development over time. 5.1. Determination of frost resistance of concrete Determination of frost resistance was carried out ac- cording to ČSN 73 1322. For the frost resistance test, the test specimens are water-saturated beams that are subjected to alternating freezing and thawing. 2 sets of test specimens were prepared for the test. One set is frozen and the other unfrozen serves as a compari- son. Freezing takes place in freezing cycles, with one cycle consisting of 4 hours of freezing and 2 hours of thawing. Once the required number of freezing cy- cles has been reached, the test is finished. The result is weight loss of frozen bodies expressed in percent, tensile strength after bending and coefficient of frost resistance. The ratio of the arithmetic mean of the strength of frozen bodies and the arithmetic mean of unfrozen beams is called the coefficient of frost resis- tance. If the frost resistance factor is at least 75 %, we can call the concrete frost-resistant [9]. All concrete formulas passed in terms of frost re- sistance coefficient, i.e. all formulas have a higher coefficient greater than 75 % (see Table 3). Some con- cretes even have a frost resistance coefficient higher than 100 %. This phenomenon can probably be ex- plained by rehydration of unhydrated cement grains. The weight loss for all manufactured recipes was a maximum of 0.88 % of the original weight of the frozen beam. Recipe A A300 L [% vol.] [% vol.] [mm] CEM I 42.5 R (sc) Mokrá 6.6 3.5 0.19 CEM II/A-S 42.5 R Mokrá 6.2 4.1 0.21 CEM III/A 42.5 N Hranice 7.4 3.7 0.23 CEM II/C-M (S-LL) 42.5 N Hranice 7.5 3.1 0.19 CEM II/A-LL 42.5 R Radotín 6.9 3.5 0.22 CEM II/B-M (S-LL ) 42.5 N Radotín 7.3 4.2 0.18 Table 3. Characteristics of air in hardened concrete (A – pore volume, A300 – volume of effective pores, L – distribution of air pores). 5.2. Air content in hardened concrete The essence of the test to determine the character- istics of the air pores in hardened concrete, their mapping is possible based on an approximation to get an approximate idea of the amount of pores in the aerated test samples.The air pore structure is deter- mined by scanning along a series of measuring straight lines, parallel to the original top surface of the sample. Number of air of pores intersected by measuring lines are recorded, as are the individual lengths bowstring. Mathematical analysis of the recorded data then en- ables a description of the system air pores in terms of the required parameters. The measurement is carried out on a cut-out from the test body, which can be seen in Figure 2. Figure 2. Prepared body for determining the air content in hardened concrete. 68 vol. 47/2024 Production of concrete pavements using mixed cements The characteristics of air pores in hardened concrete were determined on the test specimens, see Table 3, namely the total air content, the content of micro- scopic pores up to 300 µm and the spatial distribution of air pores. The total air content in the hardened concrete was in the range of 6.2–7.5 %. The effective microscopic air content of A300 ranged from 3.1 to 4.2 %. The spatial distribution of air pores was in the range of 0.19 to 0.23 mm. All these indicators assume that the designed concretes with different cements will resist weather effects, especially frost. 6. Discussions From the results of the short-term (2 and 7 day) strengths of the individual formulas, as expected, the formula with road cement from Mokré achieved the highest value of compressive strength. The lowest val- ues were achieved by cements with the lowest clinker content in the cement. The most significant increase in strength between 28 and 90 days is for the test samples that contain the active admixture. This dif- ference may be due to the pozzolanic activity, which becomes apparent after a longer period than 28 days. The highest compressive strength of all concretes was achieved after 90 days of curing. As the age of the samples increased, the difference in strength values disappeared. Aeration of the concrete mixture also has a significant effect on the magnitude of the de- termined compressive strength. If the air content is higher in the mixture, the compressive strength of the concrete decreases by up to 5 % for every 1 % of air in the concrete mixture [1, 3, 5]. In terms of concrete’s frost resistance, all formu- las achieved frost resistance coefficients above 78 %. For recipes with cements from the wet plant, the co- efficient of frost resistance even reached over 100 %. A spacing factor was determined on the hardened concrete in order to compare the results with the values measured in the fresh state. Regarding the total air content A, in the fresh concrete the value was in all cases slightly lower than the value obtained from the microscopic determination of the air content in the hardened concrete. The effective microscopic air content of A300 ranged from 3.1 to 4.2 %. The spatial distribution of air pores was in the range of 0.19 to 0.23 mm. All these indicators assume that the designed concretes with different cements will resist weather effects, especially frost [3, 4]. 7. Conclusion The study deals with the issue of verifying the use of mixed cements for the production of cement-concrete covers with a focus on reducing the carbon footprint and increasing durability and reducing the overall costs for the construction of transport structures. From the information obtained, it follows that for the production of cement-concrete covers they could also use cements with a lower clinker content and re- placement of admixtures. Blast furnace slag is among the most suitable admixtures for road concrete that can replace cement. In addition to mechanical prop- erties, other aspects such as ecology and financial complexity are currently being monitored. As the requirement to eliminate the volume of CO2, the largest producers of emissions of which are industries, is currently being increased, cement production in particular is energetically demanding, for this reason possibilities are being sought to reduce the amount of cement required without negatively affecting the properties of the proposed concrete structure. In order to eliminate emissions, the use of waste raw materials such as blast furnace slag is suitable. It is possible to replace cement with micro-ground limestone even though it is not a waste material. Acknowledgements The paper was written in the framework of the BUT specific research project FAST-J-23-8400: Verification of the applicability of mixed cements for the production of concrete pavements. References [1] X. Fu, Y. Li, C. Lin, et al. Strength, durability and appearance of low-carbon fair-faced concrete containing multiple mineral admixtures. 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Construction and Building Materials 400:132703, 2023. https: //doi.org/10.1016/j.conbuildmat.2023.132703 70 https://doi.org/10.1016/j.conbuildmat.2023.132703 https://doi.org/10.1016/j.conbuildmat.2023.132703 Acta Polytechnica CTU Proceedings 47:66–70, 2024 1 Introduction 2 Aims 3 Methodology 4 Used raw materials 5 Experiment 5.1 Determination of frost resistance of concrete 5.2 Air content in hardened concrete 6 Discussions 7 Conclusion Acknowledgements References