Elastic Work and Fracture Energy of Concretes Made with Crushed Stones and Pebbles Aggregates

Abstract

This work examines the elastic work and fracture energy of a mortar and two concretes using the wedge splitting method to attain stable crack propagation. A comparison was made of the fracture energy in mortar and concrete using two different aggregates: crushed stone and pebbles, both with sizes between 4.8 and 9.5 mm. The mortar was made of sand, Portland cement and water, using a cement: sand ratio of 1:2. The water content was 0.46 of the cement mass. The samples were molded and then cured for seven days at 25oC in 100% relative humidity. After curing, the samples were dried at 55oC for 48 hours. The concretes were produced using the same procedure, but with the addition of the aggregates. The amount of aggregate was 10 wt.% of the total weight of cement plus sand. After curing and drying, the samples were subjected to the wedge splitting procedure. The tests were carried out at a constant displacement rate of 0.030 mm/min. The following results were obtained: elastic work: 80.4 ± 0.6, 114 ± 9 and 110 ± 12 mJ, and fracture energy: 30.3 ± 0.6, 40 ± 1, and 40 ± 5 J.m-2, respectively, for the mortar and for the concretes containing crushed stone and pebbles. These results allow us to conclude that the aggregates improved the elastic work and the fracture energy of the concretes. However, the type of aggregate did not make any difference to the properties. These findings contradict what is generally known, i.e., “that concrete produced with pebbles is inferior to concrete made with crushed stone”, at least insofar as it concerns the energies associated with the fracture process.

Study of the fracture behavior of mortar and concretes with crushed rock or pebble aggregates

“…Concrete, the second most widely used material worldwide, can be defined as a macroscopically heterogeneous material whose properties depend on its phases, on their relationship to each other, and on its constituents [1][2][3][4][5][6][7][8] . The materials commonly used for the production of concretes are Portland cement, sand, aggregates, additives and water.…”

“…The wedge splitting method was patented in 1986 by Tschegg 26 and since then numerous studies have focused on improving this test, which is currently performed with well designed and accurate devices, as well as highly accurate testing machines. This favors the stable propagation of the crack, a thermodynamic condition of transformation of elastic energy stored in the testing machine and the sample into surface energy per unit of newly formed crack surface 5,[27][28][29][30][31][32] . Fracture energy, which represents the energy per unit of the fracture area of mortars and concretes, can be calculated by the following equation …”

“…The value of the integral Pds, which is determined by integrating the area under the load-displacement curve, indicates the total work of fracture. The fracture energy results reported in the literature vary significantly because the authors of these studies used different compositions, raw materials, preparation conditions and methodologies to measure the materials' properties 3,5,8,10,12,13,14,16 . The results may vary, for example, from 10 to 200 J.m …”

Influence of Crumb-Rubber in the Mechanical Response of Modified Portland Cement Concrete

“…During the fracture evolution in concrete, there is a release of energy [18,19]. Behaviour like that shown in Figure 1 [17] is typical for quasi-brittle materials like concrete.…”

Investigação da propagação estável de trinca pelo método da cunha em refratários: tijolo e concreto

“…A geometria e as medidas do corpo de prova para esse teste podem ser vistos na Figura 4.24, em que a força F M é transmitida do atuador da máquina de ensaios para a cunha. A cunha transmite essa carga para os dois roletes laterais e estes para os encostos, que produzem as forças horizontais, F H , na amostra sob teste, abrindo a boca da trinca (16,24,41,44,45,57,58) . (44,45,49) : Em muitos trabalhos, os autores apresentam a energia de fratura na forma da seguinte equação (24,44,45,59) : (27,60,61) .…”