International Concrete Abstracts Portal

Metallic soaps are salts from long chain fatty acids and they are popular as waterproofing due to their low cost and effectiveness. A detailed investigation on the mortar specimens made with different chemical additives based on Na oleate, Ca stearate – Na oleate, Al stearate and Ca - Na laurate has been performed. The additives analyzed present a different mechanism of action: Na oleate has a strong effect on the development of mortar microstructure while Al stearate or Ca - Na laurate leaves the microstructure very similar to that of the reference samples. The experimental evidences, by measuring the porosity, the water absorption, the mechanical properties and the morphology, confirm these internal structures in the mortars.

Mix-design of self-consolidating concrete (SCC) with construction and demolition concrete waste (C&DW) as recycled aggregates is investigated. The novelty of this paper consists in the possibility of using both fine and coarse high-grade C&DW for the preparation of new SCC. The effects of recycled aggregates on porosity measurements and mechanical investigations combined with time-dependent properties are investigated. A reference SCC mix, with natural aggregates and the same water/powder ratio as SCC with recycled aggregates, is reported for comparison. Results are correlated in an integrated approach to study the feasibility of structural SCC with medium-high mechanical strength. Finally, this work attempts to strengthen the concept of sustainability in civil constructions.

In the prospect of reducing CO2 emissions and landfilling of waste materials, the preparation of sustainable mortars by alkali activation was studied. According to EN 1504-3:2005, geopolymeric and cementitious mortars belonging to different strength classes (R1 ≥ 10 MPa (1450 psi), R2 ≥ 15 MPa (2175 psi) and R3 ≥ 25 MPa (3625 psi)) were tested and compared. Geopolymers were obtained with fly ash or metakaolin and a blend of sodium silicate and NaOH (or KOH). Mortars were tested in terms of workability, dynamic modulus of elasticity, drying and restrained shrinkage and porosimetry. Durability was also investigated in terms of water vapour permeability, capillary water absorption and corrosion of possible embedded rebars during the curing period and wet-dry cycles in 3.5% NaCl solution. Results showed that geopolymers are subjected to higher drying shrinkage but lower restrained shrinkage than cementitious mortars. Water vapour permeability was higher in geopolymers and capillary water absorption was lower especially in fly ash geopolymers than those of cementitious mortars. During the first month, the high alkalinity of geopolymers extends the active state of both black and galvanized steel bars. However, when exposed to chlorides, fly ash geopolymers offer a higher protection to reinforcements than cementitious mortars.

A novel self-healing system for cement composites is proposed in this study. It is based on the use of extruded cementitious hollow tubes filled with a liquid healing agent to be added in cement composites during mixing. These tubular capsules were characterized in terms of flexural strength, liquid storage capability, mixing survival effectiveness and releasing ability upon crack formation. The suitability of a specific mono-component liquid healing agent – a sodium silicate solution – was also assessed. Finally, the self-healing effectiveness of the proposed system was verified using a three-point-bending procedure to induce crack formation on laboratory scale specimens and to evaluate their mechanical recovery after self-healing. Positive results were achieved, though further research is needed to reach a final optimization.

Simply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3x2.2x0.15 m [51x87x6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear – to the advantage of durability – while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown – once more - to markedly improve slab performance, with little or no extra cost.