1. Introduction

Global annual production of cement accounts for about 5% of the total anthropogenic CO2 emission [1]. About 4.2 GJ energy is required to produce 1 metric ton PC, resulting approximately in 0.8–1.0 metric ton of CO2 release into the atmosphere [2]. A second problem besides CO2 emissions is connected with the negative ecological and health impact of red and brown mud ponds in the manufacture of aluminium-containing high-alkaline waste water rich in NaOH. Landfilling of this hazardous waste raises other problems due to the high concentrations of heavy metals and the variety in chemical composition depending to a large extent on the season and weather conditions. The main task of the current research is the development of less energy-intensive but more ecological cements. One solution is the production of innovative cement binders like alkali-activated cements, geopolymers and hybrid alkaline cements with Portland clinker addition [3, 4]. The hybrid alkaline cements have various compositions of alkali-activated aluminosilicates with low Portland clinker content [5]. In spite of the low clinker content, the hybrid binders can obtain useful early-age mechanical strengths [6]. Hybrid cements take advantage of the material properties of a cement and ordinary geopolymer with the resulting benefit on the acquired properties, so that hybrid cement can replace in large quantities energy-intensive PC [7]. The novel hybrid cement H-Cement is produced on the base of industrial by-products and wastes according to the patent application [8]. The content of clinker is always under 30 wt%. A typical feature for H-Cement binding phase formation is the combined effect of hydraulic properties of Portland clinker, pozzolanic properties of fly ashes, latent hydraulic properties of granulated blast furnace slag (GBFS) and geopolymeric properties coming from the alkaline inorganic polycondensing reactions of aluminosilicate materials. Such inorganic material is activated by addition of alkaline waste water separated from the caustic red mud ponds and Na2SO4 obtained from alkaline waste water neutralization by H2SO4. In the presence of these alkaline agents, the pH value of cement mixture is increased. This results in fly ash (FA) and GBFS dissolution leading to final geopolymerization effect. At the same time, Ca(OH)2 addition coming from Portland clinker hydration promotes the binding reactions of fly ash and GBFS. H-Cement is characterized by lower early strength and hydration heat but higher long-term strengths. H-Cement possesses high chemical resistance against aggressive action of sulphate, magnesium, chloride and acidic waters [9]. When autoclaving at an elevated temperature and pressure, H-Cement provided volume stability and strength increase in concrete with steel slag replacing a natural aggregate as opposed to PC concrete with steel slag which was disintegrated after the test [10].

H-Cement is according to internal standard. The cement was used in combination with river aggregates of 0/4, 4/8 and 8/16 mm fraction from Jelka (Slovakia). For the tests with steel slag, the river aggregate was completely replaced by the slag of the same fraction. All river aggregate properties met the requirements of STN EN 12620+A1 [14]. The compatibility of H-Cement was verified with seven types of plasticizers [15]. The concrete without admixture was examined as a reference. The shrinkage-reducing ability was confirmed on the concrete made from H-Cement, PC and selected blended systems [15]. The H-Cement suitability for mitigating alkali-silica reaction was verified on the cement mortars by the procedure reported in STN 721179 [16] (the related ASTM Standards: C289-03 for Chemical method; ASTM C1293-08b for length change of concrete). Resistance to sulphate and higher

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

temperature/pressure attack was verified by own methodologies [10, 17].

resistance and volume stability of steel slag concrete.

verification is given separately for each test.

DOI: http://dx.doi.org/10.5772/intechopen.88060

2.4 Testing procedures for cement

dynamic elasticity modulus [28].

2.6.1 Materials

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Specimens of ready-mixed concrete were made according to STN EN 12390-2 [18]. Fresh concrete was compacted on a vibration table (40 Hz) for 60 s and casted into 150 mm cubes or 100 100 400 mm prisms. Casting of the specimens for verification of specific properties of H-Cement is reported separately for each experiment, either shrinkage-reducing or ASR-mitigating property, sulphate

The moulds were stored at more than 95% relative humidity of air (abbreviated as RH) at (20 1)°C for the first 24 h, and then the concrete specimens were cured according to the test. A method of treating the specimens for special properties

Both cements were tested for chemical composition by STN EN 196-2 [19]; the Bogue mineral composition was also determined. Standard consistency, initial and final setting, and soundness were verified by STN EN 196-3+A1 [20] and hydration heat by STN EN 196-8 [21]. After 2-, 28- or 90-day cure, flexural and compressive strengths of the mortars with cement-to-sand ratio 1:3 by weight were obtained according to STN EN 196-1 [22]. H-Cement is sensitive to excess of water; the PC

The consistency of fresh concrete was estimated by slump by STN EN 12350-2, volume density by STN EN 12350-6 and air content in the fresh mixture by STN EN 12350-7 [23–25]. Concrete specimens were tested for cube compressive strengths [26], compressive strengths of the edges of prisms of standard size [27] and

Cement CEM I 42.5 R (PC) produced by Považská cementáreň, a. s., Ladce cement plant (PCLA) and C3A-free sulphate-resistant CEM I 42.5 R-SR O (SRC)

and H-Cement mortars therefore differ in water-to-cement ratios.

2.5 Testing procedure for fresh and hardened concrete

2.6 Partially accelerated test of sulphate resistance

2.2 Casting

2.3 Curing

The production of H-Cement does not require additional heat treatment. It is cured in the same way as traditional cements and owns the certificate of conformity [11] issued on the base of SK Technical Assessment [12]. H-Cement is a sustainable cement which, due to its material composition, does not meet the categorization of cements according to STN EN 197-1 [13].

This article shows that one possible solution for innovative binders with improved durability and decreased energy requirements is the production of hybrid cement. It is demonstrated that:

