P p"Gheorghe Asachi" Technical University of Iasi, Faculty of Civil Engineering and Building Services, 1, Prof. Dimitrie Mangeron Blvd

Results and discussions

The density of concrete with fly ash and polystyrene granules varies between 1880 and 2131 kg/m³. All values are smaller than the initial state of control mix that was 2250 kg/m³. Three of five compositions have density of lightweight concrete, Table 2.

Table 2. Density of concrete with polystyrene
Concrete mixes	Density [kg/m^3]
CC1	2250
FACC1	2134
FACC2	2076
FACC3	1997
FACC4	1942
FACC5	1880

Workability of fresh concrete increases when using a higher polystyrene dosage, even if the granules were not treated before mixing.

1. 
   Compressive strength
   

Fig. 1. Variation of compressive strength of concrete with polystyrene.

With the increase of polystyrene dosage as a replacement for the mineral aggregate, compressive strength decreases, in comparison with the control mix, as shown in Fig. 1. The highest values of compressive strength for all

types of concrete with fly ash and polystyrene were obtained for concrete type FCCP1, but it is smaller than that of the control mix. The decrease of strength varies between 47.7% for FACCP1 and 75.4% for FACCP5.

2. 
   Flexural strength
   

Fig. 2. Variation of flexural strength of concrete with polystyrene.

1. 
   Failure surface of FACCP1 b) Failure surface of FACCP2 c) Failure surface of FACCP3
   

d) Failure surface of FACCP4 e) Failure surface of FACCP5

Fig. 3. Failure surface by flexure of concrete with polystyrene granule.

Results obtained for f_ti underline that all values of concrete with polystyrene are smaller when compared to the control concrete sample according to the output presented in Fig. 2. The highest value is associated with the use of concrete with 20% polystyrene (FACCP1) as strength decrease is of 12.6%. The smallest value of f_ti is for the mix with maximum replacement of aggregate as the decrease reaches 44.5%.

In Fig. 3 distribution of polystyrene granules in the concrete mass is not uniform. Therefore, flexural strength depends on the presence of polystyrene granules in the tested section as granules could have negative influence on the behavior in flexure.

3. 
   Split tensile strength
   

Fig. 4. Variation of split tensile strength of concrete with polystyrene.

1. 
   Failure surface of FACCP1 b) Failure surface of FACCP2
   

c) Failure surface for FACCP3 d) Failure surface for FACCP4
e) Failure surface for FACCP5

Fig. 5. Failure surface in split tensile test of concrete with polystyrene granules.

The obtained results for f_td indicate that all values for concrete with polystyrene are smaller than that of the control concrete sample as it is underlined in Fig. 4. The highest value is obtained for concrete that contains 80% polystyrene (FACCP4) as strength decrease is 14.5%. The smallest value of f_td is associated with the scenario when mixing FACCP2 with 40% replacement of aggregate. In this case, strength decrease is about 44.2%. The smallest value of f_td is close to the other values, but this strength is evidently influenced by the distribution of polystyrene granules in concrete structure as it is presented in Fig. 5.

Following the results of the experiment related to mechanical strengths, the highest decrease is noted in compressive strength. As for tensile characteristics, values are closer to those of the control samples, which indicates a good behavior in tension. Concrete with a high dosage of aggregate substitution is recommended to be used as non-structural concrete.

4.