تأثير نسبة الماء للإسمنت على سلوك الاضافات الكيميائية

Abstract

In hot regions in general, and Libya in particular, interaction with the surrounding environmental factors has a significant impact—either positive or negative—on the properties of concrete mixtures. Chemical admixtures play an important role in controlling these properties, such as compressive strength and long-term durability. This interaction includes transportation, casting, and curing, alongside the correct and optimal use of chemical admixtures. Achieving the desired concrete performance requires a precise understanding of these processes. Chemical admixtures come in various types and interact physically and chemically with cement at early stages, which may affect their performance either positively or negatively. Therefore, it is essential to study the compatibility of these admixtures with the type of cement used, in addition to considering the surrounding environmental factors and determining the optimum dosages to avoid any adverse effects on concrete properties—particularly compressive strength, workability, and setting time. This study investigates, both theoretically and experimentally, the effects of different water-to-cement ratios and the timing of superplasticizer addition when using chemical admixtures classified according to ASTM C494 standards, including: ◼Type A    ◼Type F  ◼ Type G, The focus was on three key concrete properties: workability, which reflects the characteristics of fresh concrete; compressive strength, which indicates the properties of hardened concrete; and setting time, which marks the transition from fresh to hardened state. The findings revealed that both the water-to-cement ratio and the timing of admixture addition significantly influence admixture behavior, with noticeable differences between normal and high-range water reducers. The study emphasizes the need for laboratory testing to determine the optimal dosage that ensures compatibility between the selected admixture and the type of cement used.