română MIRCEA BÂRNAURE, CONSTANTIN DORINEL VOINIȚCHI, FĂNICA VIRGINICA PANAIT
Abstract
In this experimental study, six lime-based mortar compositions were prepared under laboratory conditions, with sand-to-lime putty volume ratios of 1, 2, 3, 4, 5, and 7. The specimens were subjected to accelerated carbonation and subsequently tested. Compressive strength tests on standard samples revealed values significantly higher than those specified in the current Romanian design and assessment regulations for the same composition. Tests performed on non-standard specimens, with reduced height - close to that corresponding to the thickness of the mortar joint - yield very high measured values, making it difficult to establish correlations between these and the strengths obtained on standardized specimens. Chemical analysis proved to be a feasible method for evaluating mortar strength, provided that the aggregate does not contain calcium carbonates. The surface hardness method does not seem appropriate for lime mortars, as the recorded values are too low. For the penetration resistance tests and fastener pull-out tests, the measured values are very scattered, so these methods do not seem reliable for low strength mortars. The Double Punch Test (DPT) appears to be a promising alternative for the determination of compressive strength on site, with experimental results showing a strong correlation with standard compressive strength values. However, tests using multiple methods on samples taken in situ are needed to estimate differences due to curing conditions, starting from chemical analysis that can provide compositional characteristics.
Keywords
mortar, lime, composition, strength, chemical analysis, double punch test
ALEXANDR MUNTEAN, CONSTANTIN DORINEL VOINIȚCHI, BOGDAN ANDREI, FANICA VIRGINICA PANAIT
Abstract
The possibility of using other types of cements, besides the unitary ones provided for by the road concrete standards, was studied. In this regard, the changes in mechanical and durability properties when replacing a CEM I42.5R cement with CEM II A-M (S-LL) 42.5R type cements and one made in the laboratory of type CEM II A-V were analyzed. Concretes made with cements with supplementary cementitious materials SCM presented better mechanical characteristics in terms of compressive strength, bending strength and wear resistance at long terms or equivalent to concrete made with unitary cement for the modulus of elasticity. Durability tests - freeze-thaw resistance highlighted a better behavior of concretes with cements with SCM compared to the standard one. The shrinkage of concrete with CEM II A-V type cement was very close to that of the reference concrete made with unitary cement; concrete made with CEM II A-M (S-LL) cement had a significantly higher shrinkage. The results are promising, opening the way to testing on a larger scale several types of cements with additives, both for classical mechanical and durability properties but also for some results from the study of specialized literature from other countries.
Keywords
blended cement, concrete, pavement, durability, mechanical strength
NICULAE NOICA, CONSTANTIN DORINEL VOINIȚCHI, RADU CONSTANTIN VOINIȚCHI, GEORGETA VOICU, FĂNICA VIRGINICA PANAIT, MADJID HADJ AMER
Abstract
Investigation of an 120 years old reinforced concrete beam were carried out in order to find the degree of degradation and other durability characteristics. The idea behind the investigations was to find compositional parameters to ensure durability based on a real-scale experiment. Half Cell Test and visual observations show good condition of the reinforcing bars despite the age of beam. Carbonation depth in some places is practically zero and further investigation presented a high pH in the concrete. Using XRD on powder from the concrete matrix we found unhydrated calcium silicates even after mare than 100 years, fact which attributed to the coarse grinding of a belite cement. This led to self-healing concrete long before the concept appeared.
Keywords
carbonation, durability, old, concrete, cement
SEDIGHEH HOSSEINI , HOSSEIN MOHAMMADI MANESH, SAYED YASSIN MOUSAVI
Abstract
This paper investigates the effect of combined calcium nitrate tetrahydrate (CN), calcium formate (CF), and silica fume (SF) on early-age compressive strength in Portland cement mortar. For an appropriate mix design with limited numbers of trials, a Taguchi experimental design was conducted. CF was added at 0.5%, 1%, and 1.5%, CN at 1%, 2%, and 3%, and SF at 5%, 10%, and 15% as partial cement replacements. Compressive strength measurements, XRD, FT IR, and FESEM provided information on hydration products, phase transformations, and microstructural densification upon hydration. The optimum mix of 1% CN, 1% CF, and 5% SF improved the 7-day compressive strength by 16.1% over that of the control. CF favored the development of C-S-H by formate action; CN accelerated hydration through the provision of calcium ions, and SF reduced porosity by pozzolanic reaction and filler action. XRD and FT IR showed a decrease in portlandite, while FESEM presented a denser matrix. Accordingly, the results suggest a feasible way to enhance the early performance of cement mortars by adjusting CN, CF, and SF contents.
Keywords
Portland cement, silica fume, calcium nitrate, calcium formate, compressive strength