Compressive Strength of Concrete

for the tests. The alkali content expressed as Na2O equivalent in both cements was estimated. From this content, the amount of NaOH required to achieve the desired Na2O eq. (1.30 + 0.05)% wt. by the standard was calculated. The tap water was enriched with a calculated amount of NaOH during laboratory production of the mortars. Prediction criteria of andesite aggregate susceptibility to ASR are given in Table 9. The composition of mortars for 6-month length change test cured at 20 and 40°C/100% RH moist air took into account the requirements of the above standard. Length changes are illustrated in Figure 3.

fact, water-to-cement ratio of HC mortar is 0.42 compared to 0.5 of PC mortar when both are adjusted on the same consistency of 140 1 mm. H-Cement shows plasticity effect in the mortar; however, it is unable to reach the strength level of both reference mortars, as reported in Table 10. The second reference mortar was prepared from C3A-free industrially made Portland cement (abbreviated as SR). HC and PC mortars were adjusted on the same consistency; that of SR differs. SR and

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

Chemical composition of PC and HC mortar after 28-day basic curing in water at

Dynamic modulus of elasticity (DME) of mortars after 5 years of exposure in the sulphate and water environment is shown in Figure 4. No evident changes were

> Initial and final set (min)

Compressive strength (MPa)

2 days 28 days 2 days 28 days

) Air content (% vol.) w/c

Flexural strength (MPa)

The cements confirm a substantial difference, especially in CaO content, also evident in Al2O3 and detectable in Na2O eq. amounts. Low CaO in hybrid cement is a prerequisite for the increased chemical resistance. Higher levels of Al2O3 and Na2O eq., as opposed to PC mortar, induce the occurrence of the alkali-activated binder based on pozzolanic components as an inorganic polymer characterized by a

binder potential alongside the minor portion of hydrated PC clinker.

Standard density (% wt.)

HC 1.95 696.8 33.0 230/285 14.9 39.0 4.1 7.8 SR 0.03 354.9 27.2 185/225 26.2 52.8 4.7 8.4 PC 14.31 344.7 25.8 220/285 26.5 56.5 5.4 8.5

HC mortar 141 2200 5.2 0.42 SR mortar 186 2210 6.3 0.50 PC mortar 142 2240 4.7 0.50

Constituent PC mortar (% wt.) HC mortar (% wt.)

Ignition loss 9.43 6.79 SiO2 64.69 71.50 CaO 18.07 6.38 Al2O3 1.86 7.91 Fe2O3 1.17 2.28 MgO 3.54 3.37 SO3 0.98 1.17 Cl 0.03 0.02 Na2O eq. 0.09 0.41

Differences in chemical composition of PC and HC mortar after basic curing.

PC were produced with the same w/c ratio of 0.5.

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

Specific surface area (m<sup>2</sup> /kg)

Mortar Consistency (mm) Bulk density (kg/m<sup>3</sup>

(20 1)°C is listed in Table 12.

C3A content (% wt.)

Basic properties of the cements.

Properties of fresh mortars.

Cement kind

Table 10.

Table 11.

Table 12.

137

The results show that H-Cement is characterized by ASR-mitigating property. H-Cement mortar (abbreviated as HC 20 and HC 40), in contrast with PC (abbreviated as PC 20 and PC 40), clearly reduces the expansion markedly below the maximum allowable standard limit [16] of 0.1% (<1%) regardless of the long-term treatment. ASR-mitigating effect under maximum allowable limit of 0.1% (<1%) is confirmed also for the blended cement consisting of 70% wt. PC and 30% wt. HC (abbreviated as HM 20 and HM 40 in Figure 3).

The contemplated cause of ASR mitigation is the presence of alkali-activated pozzolans in the substitution of up to 80% by weight of the PC clinker, which could prevent the expansion [31]. The cause of ASR is a complicated problem and is still not fully understood. In this research focused on the need for industry, the achieved effect was investigated, and its cause is not studied in detail.
