Stone made structures & Listed buildings

The methodology for current strength assessment/evaluation of stone made structures has presented over the last years a remarkable grow from the structural designing to the construction details. It is highly specialized and requires a large scale of Engineering potential as to follow the latest assessment methods and the different categories of materials as well as the structural designing via finite elements. Mostly though, the proposing engineers or the applicator has to understand the way a stone made structure behaves throughout time.

The latest is the most important characteristic since it is not rare the fact that in many cases a wrongly processed rehabilitated stone made structure tends to be more questionable as to the final condition than before the repair works.

According to the experience of the CERS Engineers team, a critical factor to a failing stone made structure is the structure of the stones themselves. The stones do not behave as a homogenous structure/material such as concrete or steel. The structural failures that occur are due to a large number of causes, where the rehabilitating Engineer is obliged to understand the reasons that lead to failure and conclude to the structural behavior pointing the weak parts of the structure.

The key factors that need to be defined are:

1. The exact stone walls width and the way they were built, that is whether the walls are made of 2 or 3 layers of stone or as a solid wall.

2. The diaphragmatic behavior on top of each level (concrete slab or perimetrical beams).

3. The existence of inner or outer vaulted ceiling areas.

4. The direction of any occurred cracks and their position relevant to the corners of the structure.

5. The existence of wooden roof and its filling material.

6. The way of stone structure at the corners of the building and the size of the corner stones that tend to differ from the rest of the walls.

Binding Stone Wall Mortar

It constitutes the basic binding material, it ensures the homogeneity of the wall and ensures the smooth transmission of the structural tensions.

Prior to any testing, designing or constructing, a chemical analysis of the binding mortar should be conducted so as to know the current condition, to define the current properties and mostly to decide the kind of proposed injection mortars for the rehabilitation process.
CERS team of Engineers having completed an important number of similar projects, from stone made listed buildings to pre Byzantine Churches is in the position to propose the suitable kind of injected mortar mix design. The final call has to do with the desired compressive strength of the mortar and its compliance with the pre existing bonding mortar.

Non Destructive Testing
By use of the non destructive testing methods CERS can measure two useful characteristics. Firstly, the surficial hardness of the stones (rebound hammer) and secondly the homogeneity of the wall and the investigation for cracks, cavities etc. (ultrasound pulse velocity – endoscopy).
In all cases of stone walls rehabilitation CERS reveals parts of the wall from any masonry (about 1,00 m2 each) so that to conduct the above referred tests and proceed to the "pathology" of the stone walls.