2.6.2 Specimens, casting and curing

Mortars with cement-to-sand ratio of 1:3 by weight adjusted on the constant consistency of 140 1 mm were prepared as prismatic specimens of size 40 40 160 mm. All specimens were kept for 5-year exposure in 5% wt. sodium sulphate (Na2SO4) solution and water as reference medium after 28-day water curing (BC) at (20 1)°C. The tests of chemical resistance were conducted by own methodology of "partially accelerated test" based on keeping the mortars in strongly over-concentrated aggressive solution for a sufficient long time. The aggressive storage was specified by the following way: each 1 cm<sup>2</sup> of the exposed area of prism must be in permanent contact with at least of 10 cm<sup>3</sup> of 5% wt. Na2SO4 [33802.8 mg aggressive SO42 per 1 litre solution]. The sulphate solution and reference water were refreshed every 30 days within 90 days of testing, every 45 days between 90 and 365 days and every 60 days up to 5 years of exposure, respectively.

### 2.6.3 Items of investigation

Consistency, density and fresh air content of the mortars were determined according to relevant STN EN Standards. The mortars were continuously tested for length changes, dynamic modules of elasticity (DME) and periodically flexural and compressive strength. After destructive tests the microstructure and pore structure were identified by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) techniques. The ground material was sieved through a 0.063 mm mesh to receive the powder suitable for testing. For the X-ray diffraction, the Philips diffractometer was used in a 2Θ range of 5–65°. CuKα radiation and Ni filter were applied. Thermal analysis was performed on the Netzsch apparatus STA 449 F3 Jupiter in air at heating rate 10°C/min. Basic parameters of the pore structure were identified by MIP using the high-pressure porosimeter Quantachrome PoreMaster 60 GT using small mortar fragments for testing. The JEOL 7500F was used to study microstructure by scanning electron microscopy. Chemical composition, with special emphasis on the bound SO3 content, was estimated by STN EN 196-2 [19].

#### 2.7 Concrete based on H-Cement and steel slag

Two types of binders (PC and H-Cement as HC) were chosen to prepare concrete based on steel slag. The Sika® ViscoCrete®-225 powder superplasticizer was used to improve the consistency of the fresh concrete mixture. It provides water reduction, excellent fluidity and cohesion, together with a self-compacting effect. Tap water from the water supply system was used as the mixing water.

Two mixes designated as HC concrete and PC concrete were used within the scope of the experimental research.

• HC concrete contained 0/8 mm steel slag fraction as filler, 380 kg of H-Cement, 241 kg of water, Sika superplasticizer in the amount of 0.5% of the cement weight and a retardant additive (Retardal 540) in the amount of 0.4% of the cement weight.

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

• PC concrete contained 0/8 mm steel slag fraction as filler, 380 kg of CEM I 42,5 N, 241 kg of water and Sika superplasticizer in the amount of 0.5% of the cement weight. No retardant admixture was used.

The production of the specimens used to test the properties of fresh and hardened concrete based on steel slag was carried out in two stages. The first stage involved the production of the specimens for testing cube strength after 3, 7, 14, 21, 28 and 90 days of age. The second stage involved the production of the specimens for the comparison of cube and prism strengths after 28 days of curing.

The following properties of hardened concrete were tested: cube and prism concrete strengths. The durability of the concrete based on steel slag was tested in the conditions of a higher temperature and pressure. Determination of the volume changes of the concrete was carried out in a 540-l laboratory autoclave at the maximum saturated steam pressure of 1.2 MPa and a maximum temperature of 189° C. Cubes of 150 mm were used as the test specimens. The temperatures and pressures in the testing laboratory autoclave were set by this way to determine the volume changes of the concrete based on the steel slag as aggregate [10].
