Analysis of a Large Database of Concrete Core Tests with Emphasis on Within-Structure Variability

Abstract

In reinforced concrete (RC) structures, the compressive strength of concrete can play a crucial role in seismic performance and is usually difficult to estimate. Major seismic codes prescribe that concrete strength must be determined essentially from in situ and laboratory tests. Mean values obtained from such tests are the reference design values when assessing existing structures under seismic actions. The variability of concrete strength can also play an important role, generally requiring that various homogeneous domains are identified in a single structure, in each of which a specific mean value should be assumed as representative. This study analyzes the inter- and intra-variability of the concrete strength of existing buildings using a very large database made up of approximately 1600 core tests extracted from RC buildings located in the Basilicata region (Southern Italy). The analysis highlighted that concrete strength variability was dependent on the structures’ dimensions as well as on the number of storeys. Moreover, the concrete strength of cores extracted from columns was found to be, on average, lower than that from beams, thus justifying the usual practice to extract cores mainly from columns, which results in a conservative approach as well as a more feasible one. Finally, some case studies were analyzed, specifically focusing on the effects of the within-storey variability. Conservative strength values, to be used especially in the case of vertical members subjected to high axial loads, are suggested.

Performance Evaluation of Plastic Concrete Modified with E-Waste Plastic as a Partial Replacement of Coarse Aggregate

“…Past works also reported a similar finding of an increase in workability [ 33 , 50 , 51 ]. However, few studies [ 52 , 53 , 54 ] mentioned a decline in the workability of concrete containing plastic aggregates owing to the irregular size and shape of shredded plastic aggregates. In the present study, manufactured PCA was used with proper control over the size and shape, thus yielding higher workability with respect to mineral aggregate concrete.…”

“…Compressive strength (CS) is an essential property of concrete that measures its ability to carry loads and is considered as one of the essential parameters in reinforced concrete design [ 52 ]. The CS of cylindrical specimens containing different proportions of PCA was evaluated as per ASTM C39 [ 45 ] standard.…”

Requalification of RC Frame Apartment Buildings: Comparison of Seismic Retrofit Solutions Based on a Multi-Criteria Approach

“…In Italy, design rules can be classified according to two macro-periods, pre-and post-1971 [34]. The former is generally characterized by low-quality concrete [35] and smooth steel [36]. On the contrary, in the early 1970s, two fundamental laws (n. 1086, 5 November 1971 [37] and n. 64, 2 February 1974 [38]) were enforced to guarantee better construction quality of structures, while materials with better mechanical properties were generally adopted.…”

“…• Concrete was assumed to have mean cylinder compressive strength equal to f cm = 20 MPa, which is in accordance with typical values for RC buildings constructed between 1971 and 1982 [35].…”

The Effect of the Composition of a Concrete Mixture on Its Volume Changes

“…One of the most common micro-defects of cement composite is the formation of micro-cracks due to excessive volume changes and the production of hydrating heat. Thus, it can be said that the good mechanical resistance and the resulting durability of the concrete composite depends on its hydration processes and the volume changes that have taken place during this hydration [ 1 ].The resulting micro-cracks due to excessive volume changes become a place for the penetration of aggressive media from the surrounding environment into the micro-structure of concrete, which has a negative impact on the durability of the composite [ 2 ]. In addition, micro-cracks occurring on the surface of the composite adversely affect its applicability for architectural purposes.…”