Use Of Alternative Aggregates In Pavement Concrete: Research And Practice In Belgium

Alternative aggregates, including recycled (concrete) aggregates as well as artificial aggregates (such as crushed stainless steel slag), are being increasingly used in road construction in the context of a more circular economy, e.g. in base and subbase layers. As these materials are applied higher up in the structure (surface and binder courses), stricter requirements are made to allow for higher loads and the stronger influence of the environment, and the application of these aggregates becomes less straightforward. The Belgian standard specifications, for instance, allow incorporation of recycled concrete aggregates in concrete pavements or linear elements in concrete, but only if certain stringent requirements are met and only up to certain percentages of substitution of the natural coarse aggregates. Furthermore, artificial aggregates originating from stainless steel slag are not even allowed for the time being in pavement quality concrete, although a Belgian standardization working group has recently been installed to investigate this matter in more detail. This paper presents an overview of laboratory research conducted in Belgium to characterize several types of alternative aggregates and concrete mixtures incorporating them, while focusing on practical execution as well as on the durability of pavement concrete. In addition, several concomitant pilot applications in Belgium are discussed in view of future perspectives for the application of alternative (recycled and/or artificial) aggregates in road construction.

Comparative Study on Microwave Absorbing Heating Characteristics and Microwave Deicing Performance of Airport Pavement Modified Concrete

In this paper, the airport pavement concrete has been taken as the main research object, three kinds of absorbing materials, namely silicon carbide (SiC), iron oxide (Fe3O4) and graphite, have been respectively mixed into the concrete, and an open microwave testing system has been established. Based on this system, the basic mechanical properties, microwave heating characteristics, microwave deicing effect and its influencing factors of modified concrete are systematically studied. In addition, a comparative analysis of the influence mechanism of different absorbing materials on the strength and absorbing performance of pavement concrete is carried out. The results showed that the addition of SiC, Fe3O4, and graphite could effectively enhance the microwave effect of pavement concrete, and the more the addition, the more obvious the improvement. Furthermore, under the same mixing amount, the degree of improvement of microwave deicing performance of each absorbing material from large to small is graphite, Fe3O4, SiC. However, the addition of graphite will form several weak links in concrete, thereby reducing its overall mechanical properties. SiC can slightly improve the mechanical properties of pavement concrete, but it has no significant effect on the microwave absorption properties. With the addition of Fe3O4, the strength of concrete changes little, and the effect of microwave absorbing heating and microwave deicing is remarkable. In general, the comprehensive performance of microwave deicing of Fe3O4 modified concrete is optimal. This study has high scientific and practical significance, and can be widely applied to deicing projects on airports and high-grade highways.

Chloride Ion Diffusion and Durability Characteristics of Rural-Road Concrete Pavement of South Korea Using Air-Cooled Slag Aggregates

In the construction industry, the lack of supply and demand for high-quality natural aggregates is a problem. In the case of South Korea, according to data from the Ministry of Environment, it is predicted that the depletion of aggregate resources will occur in 20 years, considering the amount of aggregate used in construction every year and the amount of natural aggregate. Therefore, it is necessary to develop recycled aggregates that can replace natural aggregates for construction. The purpose of this study is to evaluate the applicability of recyclable air-cooled slag (ACS) aggregates as a substitute material for natural aggregates applied to rural-road pavement concrete. That is, the applicability of rural-road pavement concrete is evaluated by evaluating the strength and durability of rural-road pavement concrete to which an ACS aggregate is applied. Durability was assessed in terms of the chloride ion diffusion, repeated wetting-drying, abrasion resistance, impact resistance, and repeated freezing-thawing tests. The test result showed that the diffusion coefficient of the mixture to which the ACS aggregate was applied was slightly larger. In addition, the diffusion coefficient was slightly larger in the case of applying the air-cooled slag coarse aggregate (GG) than in the case of applying the air-cooled slag fine aggregate (GS). The results of abrasion and impact resistance tests of ACS-aggregate-incorporated rural-road concrete indicated that abrasion and impact resistance decreased as the aggregate content increased. The ACS retained some of the properties of the blast furnace slag. Thus, in repetitive wetting-drying tests, which can cause changes in chemical properties, the ACS aggregate increased the concrete’s long-term residual strength. In addition, the results showed that the relative dynamic elastic modulus targeting repeated freezing-thawing resistance satisfied the 80% target. The freeze-thaw resistance improved as the ACS aggregate content increased. In conclusion, the results of this study showed that the durability of rural-road pavement concrete can be improved experimentally by applying both GG and GS at the same time. Therefore, it is shown that ACS aggregates can be applied to rural-road pavement concrete as a substitute for natural aggregates.

Implementation of marble waste as aggregate material rigid pavement

The rigid pavement is used for the pavement with soft ground conditions (subgrade). On the other hand, in recent years, marble waste for civil construction has been widely used to substitute conventional materials such as fine and coarse aggregate in concrete. This study aims to optimize marble sand waste as a substitute for river sand aggregates on concrete pavements. This research creates innovation in the production of rigid pavement. The study used an experimental method to test the raw material, namely fine aggregate (river sand and marble sand) and rigid pavement testing, with various variations in the material's composition, including loading, strain, and concrete slab stress tests. The use of marble sand as a substitute for river sand affects the compressive strength of concrete. The maximum compressive strength of 34.67 N/mm² occurs at 60 % marble sand content. Calculation of the optimum level of marble sand by the regression method yielded 48.90 % with an average compressive strength of 32.37 N/mm². In terms of strain, rigid pavement concrete slabs with 60 % marble sand content showed the best performance among all specimens. The stretch is relatively small so that it is not so fluctuating, the flexibility is relatively small, and the stiffness is the highest. The strain character tends to be compressive so that the dependence on reinforcement will decrease. Dynamically at the shock load, the three concrete slabs are quite good and very far from resonance in both the traffic service load frequency and the large shock load. Rigid pavement concrete slabs with a marble sand content of 40 % show the best performance because they are damping faster and have less tension. Statically, rigid pavement concrete slabs with a marble sand content of 60 % are the best