*3.1.5 Brick tensile and compressive strength*

The average value of the flexural tensile strength was 3.64 MPa for the comparative samples, and 4.26 MPa for the frozen ones. This is given by the selection criteria into individual sets—the better bricks have been selected for freezing, but it is clear that virtually all samples have safely passed on 25 freezing cycles. The exception is sample N 3 (fb,f = 0.94 MPa), for which resonant test indicated a possible failure in the internal structure. This was indeed reflected in the bending strength test, which was significantly lower than that of the other samples.

According to ČSN 722609, the compressive strength after freezing shall not decrease by more than 15% against the declared compressive strength, in this case against the strength in the pressure of the comparative (non-frozen) bodies. The average value of the bend tensile strength was 22.6 MPa, for frozen bricks up to 24.8 MPa. This is because it is basically unrealistic to create two completely comparable sets of bricks, on the other hand, it is indicative of the excellent frost resistance of the original bricks from the bridge. According to the comparative bodies, the original bricks can be attributed to the strength of the P20 (the mean compressive strength of 22.60 MPa, minimum 19.2 MPa). From the point of view of frost resistance, when the main criterion is the drop of compressive strength, all samples have been passed for 25 cycles [5].

The material analysis confirmed the good quality of the bridge bricks and together with evaluation of the quality of the environment, it provided grounds for establishing the principal degradation agents. During the visual inspection the following failures of the bridge were identified:


#### *A Deep Review on a Historical Brick Bridge in South Moravia; Reconstruction and Assessment DOI: http://dx.doi.org/10.5772/intechopen.102602*

The historic brick bridge may serve for demonstrating the seriousness of external effects, their growing aggressiveness and the result of mutual structure environment interaction including the surrounding climatic and biological ecosystems and anthropogenous factors [5].

#### **3.2 Mechanical failures**

Mechanical failures were mainly manifested by cracking ranging from hairlines to prominent tension and shear cracks, going through the joints of brickwork masonry and stone blocks. The extent and intensity of masonry degradation of individual vaults arches varied. Some vaults' arches were damaged by prominent longitudinal cracks up to several millimetres wide which extend through several masonry layers. The respective cracks were mostly situated too close to vault edges. Other cracks mostly local non-continuous ones were situated at various points and did not follow any traceable patterns. Parapet walls were damaged by loose bricks and cracks in the footing bed joint between the vault and the wall.

### **3.3 Moisture analysis of the masonry**

In terms of dampness the foundation masonry and pillars, which were currently covered with soil, were the most stressed. The moisture penetrated the structure through direct contact with the soil of adjacent terrain. The high moisture of the masonry was detected at the side of the performed probes. There was direct flooding of the probes. Building materials were disturbed and the binder was being washed off.

Rainwater was the main reason causing the high dampness of the bridge's brickwork. The water from the bridge deck seeped into layers of the backfill up to the vault (the content of moisture reached 15% by weight on top of the vaults). On several places there is no backfill, the rainwater affected directly the vault and further seeped to its lower face. Diversion of water was supposed to be done by the brick drainpipes. Considering the state of the pipes, it was possible that water levels were locally higher within particular sections of the bridge.

One of the possible causes of collapsing of the parapet wall was saturation with water from the entire backfill due to broken and non-functional waterproofing and thus increase of active pressure on the back of the parapet wall and increase of tension on the face side, which masonry was no longer able to transmit.

A very exposed part of the bridge is face surfaces—parapet walls, cornices and masonry railings. The wind-driven rain penetrated the masonry. On the windward side, there is a synergy of negative phenomena, which caused significant degradation of the masonry due to weathering manifested by leaching of the binder and scaling of surface layers. The arches were covered with soil and airborne vegetation.

Based on the analysis the summary of reasons could be stated:

