La Sia S.r.l., an engineering company, offers a diagnostic investigation service for reinforced concrete floors aimed at identifying the phenomena of the spalling of hollowcore slabs and plaster detachment. The investigations are carried out using non-destructive techniques of civil thermography and spalling carried out by specialized personnel, Engineers and Architects, certified “UNI EN ISO 9712:2012” and “Bureau Veritas internal regulation IT-IND-REG-02_NDT.CIV”.
– WHAT IS SPALLING (CAUSES AND DANGER)-
By spalling of the floor slab, we mean the detachment and subsequent fall of the lower lining of the hollowcore slabs. This phenomenon is caused by a set of factors mainly attributable to:
-Incorrect design of the hollowcore slab. An incorrect design of the slabs causes a concentration of the state of tension in the partitions of the hollowcore slab itself with the consequent detachment of the bottom lining or the internal breakage of the slabs themselves.
-Structural design defects. Poor regularity in the plan of the floor slabs, excessive spans of the joists or thick beams lead to an increase in tension in the hollowcore bricks until the mechanical strength of the brick is reached with the consequent breakage of the same.
– Manufacturing defects. Mainly found in slabs cast on site, it consists of defects linked to the segregation of the concrete and/or to the positioning with little or no concrete cover in the joists. The phenomenon of breaking through in the case in question appears to be discontinuous and distributed in patches on the floor slab.
-Maintenance problems. Interventions repeated over the years without a real maintenance program structured over time; this is the case of false ceilings, systems and lighting fixtures that are often hung from the ceiling without particular construction devices using makeshift techniques and materials.
It is important to remember that the phenomenon almost never occurs for just one of the reasons indicated but is generally the result of the presence of two or more of the above causes.
The spalling does not pose a danger to the structure as the brick only performs the task of lightening the floor slab, however it involves an important danger for the safety of the people who frequent the premises subject to the phenomenon. Suffice it to say that the weight of the detached mass is between 20 and 40 kg/m2 and that the phenomenon is often not punctual but affects portions of the floor slab, for example for a detachment of 10 m2 there is a mass of about 300 – 400 Kg falling from the ceiling onto people and objects in the room.
– HOW THE SURVEY SERVICE IS CARRIED OUT –
The survey service offered by La Sia S.r.l. is aimed at identifying the phenomena of detachment currently in progress and at identifying the causes that have triggered or may trigger the spalling.
The investigations are made up of different moments of approach to the building and to the individual rooms. Preliminary to the survey itself is the critical historical analysis, aimed at studying the construction technology used for the construction of the building, at identifying the structural and non-structural interventions that characterized the maintenance during the life of the building; this knowledge is achieved through the study of the original projects and of the documentation found and supplied by the client.
After the drafting of an accurate and detailed investigation plan for the building in question, an on-site inspection is carried out which consists of the following operational steps:
– Preliminary visual investigation aimed at identifying deteriorations, active or previous infiltrations, crack pattern.
– Thermographic investigation for the deepening of what was found in the visual investigation and the identification of the warping and the positioning of the joists.
– Exploratory tests generally performed through small coring and endoscopy in order to confirm the typology and stratigraphy of the brick.
-Manual checking on 100% of the intrados surface of the floors with the identification of particular areas of interest that have shown uneven behavior with respect to the type of floor.
-Instrumental checking through sonic-acoustic acquisition performed in stations arranged on a grid established according to the planimetry. Furthermore, we proceed to an in-depth study of all the areas that have shown anomalous behavior during manual checking.
-Status check and load tests on the anchoring systems of all the bodies hanging from the ceiling (false ceilings, systems, and lamps).
From the analysis of the instrumental checking, in accordance with the relevant regulations and the conventions used, it is possible to identify bands of degradation analyzed with diagnostic methodology:
-Insignificant risk (floor slab in good condition)
-Low risk (visual defects or superficial micro-cracks limited to the plaster layer only; not recent and/or localized infiltrations)
-Medium risk (fissures and superficial crazing on the plaster without particular signs of deterioration, presence of infiltrations, even widespread)
– High risk (obvious detachment of the intrados with swelling of the plaster; fissures and cracks widen and/or move during checking in the areas adjacent to the damage detected; there is a real risk of material falling)
– Disruption in progress (presence of the phenomenon of spalling; evident detachment of the intrados with swelling of the plaster; fissures and cracks widen and/or move conspicuously during checking in the areas adjacent to the damage detected and there is a fall of material during the investigations)
The last step of the service consists in the drafting of tables and technical reports with the graphic and chromatic identification of the anomalies found. Through the bands of degradation listed above, single areas or entire areas affected by the phenomenon are highlighted, furthermore both the crack pattern and the infiltrations visible to the naked eye or by infrared investigation are reported.
The study thus conducted ends with conclusions and considerations that identify the possible reasons that led to the criticality, the state and extent of the anomaly found.
For further information, you can also follow the following links:
Livelli di qualificazione UNI EN ISO 9712
Sfondellamento dei solai (latero cementizi): Analisi delle cause, diagnosi e interventi
