# Improvement of ANFIS Model for Prediction of Compressive Strength of Manufactured Sand Concrete
## 1 Introduction  
In recent years, manufactured sand has been progressively used to replace natural sand in building materials [1]. This new type of material, produced by crushing rock depositions, exhibits some morphology features that are unique and cannot be found in natural sand, such as the angular and rougher texture [2, 3]. Unlike manufactured sand, the common negative characteristic while using natural sand in concrete is the alkali-silica reactions between the reactive silica components and the alkali hydroxides derived from the cement. Such reactions lead to the expansion, deterioration and even failure of concrete structural elements [4]. On the contrary, using manufactured sand is advantageous with the possibility of preselection of low silica content rocks as to avoid such alkali-silica reactions. Besides, manufactured sand could positively influence the strength and durability of concrete, mainly due to better interlocking between highly irregular particles [2] or a better bonding between steel bar and concrete [5]. Indeed, as demonstrated by [PERSON] et al. [6] in an experimental investigation, machine-made sand particles exhibit usually a higher degree of angularity than river sand particles(i.e., in terms of morphology). The same conclusion was also achieved by [PERSON] et al. [6] in terms of surface texture. Logically, they found that the compressive and flexural strengths of pavement cement concrete, as well as its abrasion resistance, have been largely improved compared to conventional sand concrete. Various other comparative studies have been introduced in the literature in proving the performance of machine-made sand such as [PERSON] et al. [7], [PERSON] et al. [8] or [PERSON] et al. [9]. Therefore, manufactured sand has currently caught great attention from researchers, as well as the whole construction industry [10; 11]. In the literature, many works have focused on the quantification of how the concrete workability and durability could be influenced by using manufactured sand [6; 12], especially its compressive behavior [1; 13; 14; 11; 1]. In a series of papers, [PERSON] et al. [3; 13] have identified the influence of the shape of manufactured sand and roughness on the concrete compressive strength based on digital image analysis and experimental compression tests. The authors have also pointed out that the stone powder of manufactured sand exhibited a considerable effect on the performance of concrete. In another study, [PERSON] et al. [6] have prepared manufactured sand concrete (MSC) samples from different petrographic sands such as limestone, quartzite, granite, basalt and granite gneiss, respectively. The authors discovered that morphology and texture characteristics of manufactured sand hugely influenced the performance of concrete. As an example of results, the flexural strength and abrasion resistance of MSC were better than natural sand concrete if the crushing value of manufactured sand particles is less than 26.5%. It was also proven in many other experimental studies that MSC exposed better compressive behavior than that composed of natural river sand [16; 17]. One of the most important parameters of MSC is the compressive strength, which is often obtained by experimental laboratory tests. However, these laboratory investigations were generally complexes, cost and time consuming. Moreover, the laboratory tests were often limited within 90-180 days periods [18]. Despite all the efforts, it was not often possible to perform too many variations of ingredients (i.e., proportion of cement, water and machine-made sand as well as stone powder content in sand). Recently, Artificial Intelligence (AI) based methods have been successfully employed in the field of materials [19], especially for predicting compressive strength of concrete [20; 21; 22; 23; 24]. [PERSON] et al.