Compression layer with structural lightweight screed mortar

Descripción sistema

La Barceloneta is a seaside neighborhood in the city of Barcelona, ​​whose construction began in 1753 and was inaugurated in 1755, with the aim of re-housing citizens who had been evicted from the Ribera neighborhood to build the citadel fortress, and newly arrived peasants who had been converted into workers.

As the first urban expansion district built outside the city walls, it was given the name Barceloneta to reinforce its identity with Greater Barcelona.

At that time, the discipline of town planning was not included in the training of architects , so the management of numerous projects was carried out by military engineers. Thus, in the case of Barceloneta, the military engineer Juan Martín Cermeño was in charge of the creation of the neighborhood, and his project applied organizational criteria characteristic of military camps, such as modular repetition, rectilinear layout and spatial clarity.

The buildings were initially single-family houses of ground floor plus 1 floor, of about 120 m2, with access to two streets for optimal ventilation. The strong demographic growth experienced by the neighborhood due to the industrialization of the 19th century led the owners of these houses to want to obtain an economic return from them and, from then on, they began to separate the ground floor from the first floor. The increase in residential pressure led to a further step in the division of the dwellings, and the “quarter houses” appeared, with dimensions of between 28 and 35 m2, which came to house families with a large number of members.

In 1839, the authorities authorized the construction of a first floor. In 1858, Barceloneta passed from military to municipal jurisdiction. In 1868, the city council authorized the construction of a third floor, and permission for the fourth floor was granted in 1872.

The house in which Molins products have been applied corresponds to one of these rooms, and is located in a PB+2 building, whose horizontal structure (floor slabs) is made up of wooden joists and ceramic vaults.

Reason for the intervention

Within the framework of the rehabilitation of the house, which included its structural adaptation, it was decided to lift some areas of the pavement where there were significant defects in planimetry , in order to proceed with their repair and leveling.
When this operation was carried out, it was found that:
“The paving, consisting of unglazed ceramic tiles, is laid on an unreinforced mortar base layer.
“The wooden joists are in apparently good condition, with a loss of section in some areas.

To carry out the repair, it was decided to replace the mortar supporting the slabs with a reinforced compression layer, made with the lightened structural screed mortar PROPAM® RECRECIDO LIGERO AR, which will allow a better distribution of the loads, homogenizing the resistant contribution of the joists as a whole.

Challenges and constraints

“Protect the wood of the joists against the action of environmental humidity.
“To prevent the water used to mix the mortar used for the compression layer from affecting the wooden joists.
“To obtain a good physical bond between the wooden joists and the compression layer.
“To obtain a mechanical performance of the compression layer of more than 30 N/ mm2 (at 28 days) with an average thickness of 7 cm of lightened mortar.

Molins Solution

“Application of a protective layer of BETOPOX® 93 on the surface of the joists.
“Once the connectors have been installed, in order to promote mechanical adhesion between the compression layer and the joists, application of a new layer of BETOPOX® 93 with a dusting of fine natural quartz aggregate while the resin is still fresh.
“Installation of electrowelded mesh for load distribution.
“Pouring of PROPAM® RECRECIDO LIGERO AR mortar to form the compression layer.

Execution

“Cleaning of dust residues from the surface of the joists, and application of a first coat of BETOPOX® 93, a two-component bonding bridge based on low-viscosity epoxy resins, with a 150 g/m2, which will act as a protective barrier against environmental humidity. BETOPOX® 93 meets the requirements of EN 1504-7.

“Installation ofconnectors to allow a better physical bond between the joists and the compression layer. Application of BETOPOX® 93 at a rate of 200 g/m2, and sprinkling of natural quartz aggregate (0.4-0.9 mm) until saturation, while the resin is still fresh. After 24 hours, sweep the surface to remove unbonded aggregate. Preparing the surface of the joist in this way promotes the bonding (mechanical adhesion) of the compression layer to the joist surface.

“3. Fixing of electrowelded mesh (Ø 5 mm, ME 15×30)

“ Pouring of PROPAM ® RECRECIDO LIGERO AR mortar (CT-C25-F5), lightweight micro-concrete, for the execution of structural screeds in thicknesses of 30 to 100 mm. It is 40% lighter than conventional concrete and complies with the requirements of standard EN 13813.
The final finish is made with a light coating.

Technical note

PROPAM® RECRECIDO LIGERO AR mortar has three fundamental advantages over conventional concrete when refurbishing old structures:
“It is 40% lighter, which lightens the weight of the structure.
“It acquires high mechanical resistance in a very short time, reducing execution times.
“It requires less thickness than concrete, which significantly reduces the loss of usable space.

The density of a conventional hardened concrete is around 2 to 2.2 kg/dm3 while the density of hardened PROPAM® RECRECIDO LIGERO AR mortar is approximately 1.2 kg/dm3. This lightness together with compressive strengths at 28 days of more than 25 N/mm2 allow structural screeds with weights between 40% and 50% lower, and therefore to rehabilitate old slabs with structural weight problems.

The low density of This mortar is achieved with a careful granulometry of light aggregates, and with the use in its formulation of a perfectly studied combination of fluidizing and aerating additives, which manage to introduce suitably stabilized and unconnected air pores into the mass, so that durability is not affected as they do not contribute to the diffusion of water or other external agents that degrade the mortar.

The screeds obtained with PROPAM® RECRECIDO LIGERO AR are also good thermal and acoustic insulators, due precisely to their content of stabilized air pores. The thermal conductivity (λ) of this screed is 0.4 W/mk.