مطالعه آزمايشگاهي تاثير مدول نرمي ريزدانه بر پارامترهاي فيزيكي و مكانيكي بتن

Experimental Study on the Effect of Aggregate Fineness Modulus on Physical and Mechanical Properties of Concrete

چكيده- از آنجايي كه حدود 4/3 حجم بتن را مصالح سنگي تشكيل مي دهد، مطالعه در مورد تاثير ويژگيهاي آن از قبيل نوع دانه‌بندي بر پارامترهاي فيزيكي و مكانيكي بتن ضروري به نظر مي رسد حال آنكه تحقيقات مبسوطي در اين زمينه انجام نگرفته است. هدف از اين تحقيق بررسي تاثير مدول نرمي مصالح سنگي ريزدانه برخواص فيزيكي و مكانيكي بتن مي باشد. بدين منظور با استفاده از 7 نوع دانه بندي با مدول نرمي ريزدانه متفاوت و 11 نسبت آب به سيمان مختلف،77 طرح اختلاط متفاوت طراحي وتحت آزمايش اسلامپ قرار گرفت. همچنين به واسطه طرح اختلاطهاي طراحي شده، 462 نمونه مكعبي و استوانه اي ساخته و در سنين 7 و28 روز تحت آزمايش مقاومت فشاري، مدول الاستيسيته و مقاومت كششي قرار گرفت. نتايج حاصل بيانگر تاثير مسقيم مدول نرمي مصالح سنگي ريزدانه برخواص فيزيكي و مكانيكي بتن مي باشد. به اين صورت كه كاهش مدول نرمي ريزدانه از 26/3 تا 66/2، افزايش اسلامپ، مقاومت فشاري، مدول الاستيسيته و مقاومت كششي بتن را به همراه دارد. عامل افزايش پارامترهاي مكانيكي بتن را مي توان در انسجام ساختار دانه بندي مصالح سنگي با مدول نرمي كمتر دانست. همچنين وجود مصالح سنگي با ابعاد كوچكتر در ساختار دانه بندي با مدول نرمي پايين تر سبب شده است تا شرايط مناسب تري براي جابجايي ذرات بزرگتر فراهم آيد كه اين امر افزايش نرخ اسلامپ را در مقابل كاهش ميزان مدول نرمي به همراه داشته است. در نتيجه مي توان گفت نوع دانه بندي مصالح سنگي به منظور ايجاد يك ساختار مناسب، تاثير بسزايي بر خواص فيزيكي و مكانيكي بتن ايفا مي كند.

Concrete is one of moderately new materials, which is used widely because of its appropriate properties. Many Scientifics and researchers have tried to develop and utilize the beneficial properties of this new material and as a result its ingredients have been investigated extensively. Concrete properties are dependent on many parameters such as ingredients, production and technology, construction methods and curing conditions that have made concrete a complex and unpredictable material. But these are virtually ignorable against its precious advantageous and precise studies on above parameters may help us to produce concretes with desirable properties. As it was discussed previously, ingredients are of those important parameters that play an essential role. Therefore investigating ingredients, their interactions and effects of their properties on properties of concrete are seriously important. Of the most important of concrete ingredients are aggregates, which are usually deemed unimportant despite their momentous contribution to concrete production. As about three forth of concreteʹs volume is its aggregates, studying aggregatesʹ properties including the effect of grain size distribution on physical and mechanical properties of concrete is pivotal, although few comprehensive and acceptable investigations have been carried so far. Shape, particle size distribution, dimensions, surface characteristics, and minerals are parameters which are effective in making a homogenous and united medium. In fact there are various parameters (criteria) which determine an ideal material. In this study, the effect of fineness module of fines aggregate on mechanical and physical parameters of concrete has been investigated among other parameters. Fineness module is defined as total accumulated percentage of remained material on standard sieves in fines range. In this study and in respect to above factors, in order to study the effect of fineness modulus of aggregates on physical and mechanical properties of concrete, using 7 different grain size distributions with various fineness modulus and 11 cement-water ratios, totally 77 different mix designs were tested for slump test. Also 462 samples were prepared using those various mix designs and were tested at 7 and 28-day life long under compressive loads. The obtained results suggest clearly the direct effect of fineness modulus of aggregates on mechanical and physical properties of concrete. In details, the decrease in fineness modulus from 3.26 to 2.66 has caused an increase in slump values and compressive strengths. The rise in compressive strength can be addressed to more unity for aggregates with smaller fineness modulus. Furthermore, the existence of smaller aggregates (smaller fineness modulus) has led to more comfortable conditions for larger grains to travel. This in turn incited the slump valuesʹ boost while fineness modulus decreased. As a result it can be concluded that the grain size distribution can play a crucial role in dominating physical and mechanical properties of concrete.