###### Abstract  
This article presents the results of research on the possibility of replacing fly ash with recycled waste glass in lower-strength concrete mixes. The results of testing concrete mixes containing either waste-glass powder or fly ash are presented in the article. A standard C12/15 concrete mix was chosen for the tests based on its common use for producing concrete for footings to support road kerbs and gutters along national roads in the Polish province of West Pomerania. In the first step of the testing procedure, reference mixes were prepared with 22.5% and 45% fly ash in relation to the content of cement. In the next step, mixes were prepared based on the same specification, except that glass powder was added in place of fly ash. The samples were then tested to determine the influence of waste-glass powder on the main properties of the prepared concrete mixes and on the performance of the concrete when hardened. All the samples were tested for 7 and 28-day compressive strength, water absorption, and freeze-thaw resistance in water. Next, the performance parameters of the samples containing waste-glass powder were compared to the reference mixes containing an equal amount of fly ash. The test results and their analysis allow us to conclude that mixes containing glass powder are not only equal to mixes containing fly ash, but even outperform them by a wide margin in terms of durability.  
waste-glass powder; fly ash; eco-efficient concrete; durability +
Footnote †: journal: Medical  
glass factories due to excessive dirt or colour variety. Such waste glass can obviously be reused if it is first subject to preprocessing, i.e., primarily cleaning, separation of coloured from clear glass, and crushing to the appropriate particle size. However, this is not an easy task because of the complicated process of separating and sorting [3]. Figure 1 shows typical waste glass preprocessing and precleaning.  
Recent publications [4; 5; 6; 7; 8; 9; 10; 11; 12; 13] indicate an increasing interest in waste glass and its application in concrete production. It is worth noting that use of glass as an addition to concrete can be limited due to the risk of alkali-silica reaction (ASR) [5; 6; 7; 13]. Some studies have demonstrated that particles of glass greater than 1 mm make concrete more prone to ASR-induced damage [7; 8]. Conversely, the addition of ground glass reduces or limits the adverse effect of expansive ASR products [13; 14; 15]. Other studies have demonstrated pozzolanic properties in concrete containing ground glass [14; 16]. There are many research projects [4; 7; 9; 10; 17] concerning concrete of C20/25 strength class and higher, in which waste glass is most often seen as a partial substitute for cement, fine aggregate, or both of these ingredients at the same time. On the other hand, there are no studies treating waste glass in the same way as other concrete admixtures, i.e., as a filler and partial substitute for cement. While improving the performance of concrete, these additions can also reduce the amount of cement and lower the production cost. The research described in this article was inspired by the promising results of experiments conducted on concrete containing waste-glass powder, as presented in [18]. That being said, the authors have attempted to replace fly ash with recycled ground glass in low-strength-class mixes, i.e., up to C20/25. In road-construction applications, mixes of this type are used mainly for the casting of footings to support precast gutters laid along roads and herbs. Currently, the only requirement for such mixes to be used on the national roads in Poland is that the concrete has a set minimum strength class. According to the requirements [19], such footings should be made from concrete with a compressive strength class of C12/15.