G Baronio

Study of the pozzolanicity of some bricks and clays

Abstract An increasing interest in the pozzolanic activity of bricks with calcium hydrate has been shown recently by researchers dealing with the production of new hydraulic materials for the masonry industry. Furthermore, deteriorated mortars of historic buildings and damaged masonries require repointing, repair or strengthening with mortars and grouts compatible with the existing materials. Admixtures of hydrated lime and crushed bricks also have an acceptable colour from an aesthetic point of view. This paper concerns a systematic research on the pozzolanicity of different bricks and clays. The laboratory tests were based on chemical, mineralogical-petrographical analyses and pozzolanicity tests, applied to measure the capacity of crushed bricks in fixing calcium hydrate (pozzolanicity). Various types of clay, calcinated at different temperatures, are subjected to the pozzolanicity test in order to state the degree of pozzolanicity. The research intends to give guidelines for the production and use of pozzolanic bricks and clays for the preparation of hydraulic mortars and grouts.

The role of brick pebbles and dust in conglomerates based on hydrated lime and crushed bricks

Abstract Phoenicians were probably the first ones to use mortars based on hydrated lime and crushed or dust bricks, followed by all other people who were in contact with them. The Romans employed those mortars any time they needed a rendering exposed to severe environment or a floor at a very humid ground level, in foundations where the water table was high or for thermal baths. The use of brick dust in a lime mortar is, nowadays, generally interpreted as an alternative to pozzolana or to other pozzolanic materials. The authors themselves have found, some years ago, clear reaction layers at the contact between the binder and the brick pebbles. Those bricks were found to be mostly pozzolanic under a pozzolanicity test. In some cases, the test gave negative results; nevertheless, the mortars were compact, strong, better than the normal putty lime mortars even when very thick joints were realized, as in the case of the Byzantine buildings. The authors are exploring the possibility of other roles played by the bricks, especially in the case of very thick joints, perhaps producing a good bond while also serving as aggregates and giving overall good physical and mechanical performances to the mortars. Some mortar specimens made from hydrated lime and crushed bricks with chosen size and distribution have been prepared together with a specimen made from large bricks and thick mortar joints. The carbonation process and the strength and deformability at different curing times is explored experimentally.

Experimental research for the choice of adequate materials for the reconstruction of the Cathedral of Noto

Abstract Following the experimental and structural investigation the design for reconstruction was proposed. The authors were requested to test new materials, stones, mortars, grouts for injection in order to choose and proposed the material to be used for the reconstruction of the pillar and for the repair of damaged elements.

On-site investigation on the remains of the Cathedral of Noto

Abstract The Cathedral of Noto was damaged after the earthquake that hit Sicily in 1990. Soon after the event, cracks appeared on the domes of the lateral naves, and also on the pillars. In 1992 some provisional work had been carried out in view of confining the pillars of the central nave that were damaged. Some pictures made after the earthquake also show clearly the presence of moisture rise on the pillars and walls. A sudden collapse due to the damages was probably not expected, so that no other measures were taken to better strengthen and repair the structures. Only after the collapse of the Civic Tower in Pavia (1989) and the following research (Masonry Int J 6 (1992) 11, Second International Conference RILEM on Rehabilitation of Structures, Highett, Australia (1998) 542), it was clearly shown that in case of high stresses on low-strength masonry an existing damage can slowly lead to partial or total collapse of the structure over a long time. It seems a confirmation of this long-term behaviour of the structures that the Cathedral collapse took place in 1996, 6 years after the earthquake, which had certainly caused high damages to the structure.

Experimental Study on the Compatibility of a Polysiloxane Treatment with Substrates Loaded with Sodium Sulphate: Influence of the Physical Properties of the Substrates on the Salt Content Limit / Experimentelle Studie zur Verträglichkeit einer Polysiloxan-Behandlung mit einem porösen natriumsulfathaltigen Werkstoff: Einfluss der physikalischen Eigenschaften des Untergrundes auf den kritischen Salzgehalt

Within the framework of an EC program on the compatibility of salt with surface treatments (COST), crystallization tests were carried out on 20 different substrates (limestone, sandstone, brick, tuffeau, tuff and plaster) treated with a polysiloxane (Rhodia H224) or untreated. First, the samples were treated with the hydrophobic agent and the impregnation depth and product consumption were measured. Crystallization tests were carried out for each material using various initial salt contents. Both visual examination of the damage and weighing of loose materials (stone and salt) collected after the test (mass loss) were undertaken to provide qualitative and quantitative test evaluations. The influence of the protective treatment on the observed deterioration depends on the type of substrate. In general, treated samples result in worse spalling or flaking than that observed for untreated specimens. The treatment modifies the way the substrate dries and prevents surface efflorescence formation. But as salts crystallise deeper within the porous network, the treated material suffers other degradation phenomena and eventually, more damage.