پديد آورندگان :
احمدي، جمال دانشگاه زنجان - دانشكده مهندسي - گروه عمران , پناهي، عليرضا دانشگاه زنجان - دانشكده مهندسي , عزيزي، حسام دانشگاه زنجان - دانشكده مهندسي
كليدواژه :
بتن با سطح عملكرد بالا , عمل آوري داخلي , سنگدانه هاي سبك وزن , جذب آب , خود جمع شدگي
چكيده فارسي :
عمل آوري داخلي بتن با سطح عملكرد بالا بوسيله سبكدانه از پيش اشباع شده به عنوان يك روش مناسب براي كاهش و يا حذف احتمالي خود خشك شدگي و خود جمع شدگي شناخته مي شود. اگرچه جايگزيني اين مواد با مقداري از سنگدانه هاي معمولي، ممكن است به خصوصيات مكانيكي مانند مقاومت فشاري بتن لطمه وارد كند. خصوصيت اصلي ماده عمل آورنده داخلي، توانايي آن در نگهداري آب مورد نياز بتن براي عمل آوري آن مي باشد. با توجه به اين خصوصيت مواد عمل آورنده معمولا مواد با تخلخل زياد و داراي مشخصات مكانيكي ضعيف هستند كه بايد اثرات اين مواد در خصوصيات مهم بتن با عملكرد بالا بررسي شود. اين اثرات و ارتباط آن با مواد عمل آوري داخلي همچنان به عنوان يك موضوع تحقيقاتي مورد توجه قرار دارد. درمقاله حاضر، سعي مي شود خصوصيات مكانيكي و پايداري بتن از جمله مقاومت در برابر نفوذ كلريدها، نفوذ پذيري هوا، جذب آب، خود جمع شدگي خشك شدگي و همچنين وزن بتن بررسي شود. نمونه ها با نسبت آب به سيمان مختلف ساخته گرديد. اثرات عمل آوري داخلي بر روي خصوصيات مربوطه به بتن با سطح عملكرد بالا به صورت تابعي از نسبت آب به سيمان بيان شده است.
چكيده لاتين :
Due to the effects of shrinkage on concrete, such as creation and propagation of the cracks in concrete volume, reduction of durability and lifetime of concrete structures, and so on; it is crucial to consider some special arrangements to confront with shrinkage strain. A suitable concrete curing is one of the effective factors in improving the durability of a concrete structure which makes them more sustainable. During the curing procedure -that is generally accompanied with sufficient water support- two major objectives are considered: 1.Hydration products and their penetration in the internal pores and consequently, reduction in porosity that increases the strength and sustainability of concrete. 2.Reduction in shrinkage and volume changes and consequently, reduction of crack probability in the concrete.
There are different methods for curing to keep the internal relative moisture of concrete in an acceptable level. External curing, is a traditional and common method for concrete curing in which the required moisture is provided by sprinkling water or using wet canvas which is sometimes not performed homogenously. To solve this problem, some modern methods such as internal curing have been developed and used in recent years. It must be noted that, in external curing for concrete element with a low water/cement ratio, water can penetrate just some millimeters inside; while in internal curing, water can be distributed in the whole parts of a concrete element.
Considering the significant role of autogenous shrinkage in the low water/cement-ratio concretes, reduction of the negative effects of autogenous shrinkage strains on the strength and sustainability of concrete are investigated in this research, by providing internal curing conditions using LECA lightweights. According to the above-mentioned, the main objective of this research is to study the effects of internal curing methods on the autogenous shrinkage of concrete and mechanical properties of the high-strength concrete. For this goal, it's tried to study the absorption specifications; also test the efficiency of internal curing agent, and study its specifications for internal curing. Firstly, some experiments –such as the determination of absorption amount- were uninterruptedly –performed on the internal curing agent as the water reservoirs. Additional tests for determination of autogenous shrinkage, compressive strength, tensile strength, chloride penetration and electrical resistance were also performed to determine the effects of internal curing on the micro-structures and effects of hydration procedure on specimens including LECA and specimens without internal curing.
The materials used in this research include Portland cement/Type I, river aggregates, LECA as an internal curing agent, and some additives. The used LECA in this experiment is classified as fine and their maximum nominal diameter is 4 mm. In all of the concrete mix designs, micro silica is added equal to 10% of cement weight. In order to reach a suitable workability, also to reduce the water-cement ratio glenium plastisizer, that is a polymer based on poly-carboxylic, is added to the mix design.
According to the obtained results, it was observed that LECA is capable to omit the autogenous shrinkage in concrete, but the presence of LECA causes reduction in concrete strength in the concrete specimens.
