PSI - Issue 23

Lucyna Domagała / Procedia Structural Integrity 23 (2019) 342 – 347 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

344

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The rest constituent materials were: Portland cement CEM I 42.5R, tap water and optionally alkali-resistant glass or polypropylene fibres and foaming agent. The compositions of prepared insulating-structural concretes are given in Table 1. The water content presented in Table 1 includes water amounts resulting from water absorption of lightweight aggregates. 2.2. Specimens and testing methods From each type of lightweight concrete 18 specimens were moulded: 6 sets of 3 standard beams 40 mm· 40 mm· 160 mm for determination of oven-dry density, as-received density, moisture content, water absorption, flexural and compressive strength tested in natural condition and after heating at different temperatures. All specimens after demoulding at the age of 24 hours were cured in air at 20 o C and 50 % RH for next 27 days. These conditions of curing correspond to those typically used in precast plants manufacturing thin-walled elements. All tests of prepared specimens of insulating-structural concretes were carried out after 28 days of curing. Determination of as-received density and oven-dry density was performed in accordance to the rules of EN 12390-7, moisture content and water absorption in accordance to the rules of EN 1338, flexural and compressive strength in accordance to EN 196-1. Each concrete property was tested on 3 specimens excluding compressive strength which was determined on 6 halves of 3 standard beams used for flexural strength test. 48 standard beams made of four lightweight concretes were subject to temperate of 100 o C, 200 o C, 300 o C and 400 o C. The resistance to high temperature was tested on specimens in the most unfavorable moist condition. Depending on the type of concrete the initial moisture content rated from 8.2 % (for LAC1) up to 30.6 % (for LAC4). The heating rate in the furnace to the pre-determined temperature was assumed according to procedure Rilem TC 200-HTC and was equal to 1 o C / min. As a result, the specimens were heated for 80, 180, 280 and 380 minutes, respectively to the pre-determined temperature of 100 o C, 200 o C, 300 o C and 400 o C. The pre-determined temperature was maintained for 1 hour and afterwards specimens were cooled to 20 °C. Then they were visually inspected for presence of any cracks and tested for density, flexural and compressive strength.

3. Results and discussion

3.1. Basic properties of composites

The mean values of basic properties of insulating-structural concretes are presented in Table 2. They differed considerably depending on their constituents materials and compositions. The oven-dry density ranged from 620 kg/m 3 for LAC3 and LAC4, made of expanded glass, to 1340 kg/m 3 for LAC1, made of natural sand, perlite and polystyrene without foaming agent. The corresponding range of compressive strength was 8.8 MPa for LAC4 to 18.6 MPa for LAC1.

Table 2. Mean values of properties of insulating-structural concretes at 28 days Concrete type Density in natural state, kg/m 3 Oven-dry density, kg/m 3 Moisture content, % Water absorption, %

Compressive strength, MPa

Flexural strength, MPa

LAC1 LAC2 LAC3 LAC4

1450 1170

1340 1020

8.2

18.2 23.1 37.8 38.3

18.6 11.5

3.7 2.5 2.1 1.8

14.7 30.2 30.6

810 810

620 620

9.4 8.8

The application of glass fibres in the case of LAC3 caused increase of flexural and compressive strength, by 17 % and 7 %, respectively, in comparison to LAC4 without fibres. The water absorption of the insulation and structural concretes was very high ranging from 18.2 % up to 38.3 %. Such high values, typical for most of insulating-structural concretes, resulted from high water absorption of lightweight aggregates itself as well as from high water-cement ratio of cement matrix and application of foaming agent.