INFLUENCE OF FIBER REINFORCEMENT ON CONCRETE SHRINKAGE FOR RIGID ROAD AND AIRFIELD PAVEMENT REPAIR

The influence of fiber reinforcement with steel anchor fiber on the shrinkage of modified concrete for rigid airfield pavements repair has been determined. A 2-factor experiment was carried out, in which the following composition factors were varied: the amount of hardening accelerator Sika Rapid 3 from 0 to 2.4% of the cement content (0-9.6 kg/m3); the amount of steel anchor fiber with 1 mm diameter and 50 mm length, from 0 to 100 kg/m3. For the concrete batching were used: Portland cement CEM II / AS 42.5 in the amount of 400 kg/m3, granite crushed stone 5-20 mm, quartz sand, plasticizer admixture BASF MasterGlenium SKY 608 in the amount of 1.2% by cement content. The workability of the mixtures was S2 (6-8 cm); W/C ratio depended on the concrete composition. Due to the use of superplasticizers, the W/C of all investigated mixtures was in the range of 0.309-0.343. The shrinkage of the prism specimens was recorded after 3 hours, 6 hours, 1, 2, 3 and 7 days of being in air-dry conditions. The shrinkage process does not end after 7 days of concrete hardening, however, the general nature of the influence of variable factors on its value remains. It has been established that fiber-reinforced concretes, with a fiber amount of 50 kg/m3 and with a fiber amount of 100 kg/m3, have 10-15% less shrinkage compared to unreinforced concretes. Compositions with a fiber amount of 50 kg/m3 and 100 kg/m3 have practically the same shrinkage, which is explained by an increase in W/C ratio with an increase in the amount of fiber reinforcement. The amount of hardening accelerator has a less noticeable effect on the amount of concrete shrinkage. By adding Sika Rapid 3, concrete shrinkage at the age of 7 days is reduced by 2-9%. This effect can be explained by the fact that internal stresses arising in the process of structure formation and moisture loss in concrete are contained in a more durable cement-sand matrix. The concrete shrinkage without fiber and accelerator was also measured up to the age of 98 days. It was found that the limiting shrinkage for such concrete is 2.5×10-4. The analysis of the drawn experimental-statistical model showed that with the amount of metal fiber from 60 to 90 kg/m3 and the amount of the hardening accelerator from 0.9 to 2.4%, the shrinkage of the investigated concretes is minimal (7 = 1.3×10-4). Thus, the use of fiber reinforcement with anchor steel fiber and a hardening accelerator can significantly reduce the concrete shrinkage for the rigid airfield pavements repair is important for this material.

A discussion for the reduction in the length of a prestressed concrete railway tie in time

Increasing train speeds, contemporary requirements for reduced track maintenance costs and extended track service lives required the development and use of reinforced concrete and prestressed concrete ties. Railway engineers began to use concrete for their bi-block and monoblock railway ties heavily, following the development of an understanding for design and performance of concrete structures, production of high strength steel wires and preferable economy of prefabricated mass production for reinforced and prestressed concrete structural elements following the first half of 20th Century. Structural elements of a railway track such as reinforced or prestressed concrete ties have strict production tolerances that are not common for ordinary structural elements. Production of concrete railway ties takes place under strict dimensional control that ensures a nominal design gauge width for the railway track. Design specifications for prestressed monoblock ties frequently specify the gauge width and the shoulder width to be within 1 mm of the design width. However, prestressed concrete ties experience shortenings in length due to transfer of the prestressing force known as instant elastic shortening and shortenings due to concrete shrinkage and concrete creep in time that also relate to ambient relavite humidity. The author conducted numerous studies on the matter, showed by calculation, and observed experimentally that if unaccounted for, such shortenings can surpass the allowed tolerances in time and result in the rejection of the produced tie for use in the railway track. This paper refers to previous studies by the author that brought international attention on the issue and presents a thorough and a practical evaluation of time related changes in tie lengths for a particular design for prestressed concrete monoblock ties under varying ambient humidity conditions.

Long-Term Concrete Shrinkage Influence on the Performance of Reinforced Concrete Structures

The contribution of concrete to the tensile stiffness (tension stiffening) of a reinforced concrete (RC) member is a key governing factor for structural serviceability analyses. However, among the current tension stiffening models, few consider the effect brought forth by concrete shrinkage, and none studies take account of the effect for very long-term shrinkage. The present work intends to tackle this exact issue by testing multiple RC tensile elements (with different bar diameters and reinforcement ratios) after a five-year shrinking time period. The experimental deformative and tension stiffening responses were subjected to a mathematical process of shrinkage removal aimed at assessing its effect on the former. The results showed shrinkage distinctly lowered the cracking load of the RC members and caused an apparent tension stiffening reduction. Furthermore, both of these effects were exacerbated in the members with higher reinforcement ratios. The experimental and shrinkage-free behaviors of the RC elements were finally compared to the values predicted by the CEB-fib Model Code 2010 and the Euro Code 2. Interestingly, as a consequence of the long-term shrinkage, the codes expressed a smaller relative error when compared to the shrinkage-free curves versus the experimental ones.

Effect of the addition of waste basalt fibers on concrete shrinkage

This article presents the issues related to using by-products and waste materials in constructionand mining industry. The current applications of selected materials in various areas are presented, with particularfocus on cases in the construction and mining industries, where waste-based composites sealed with various hydraulic binders are used to build new structural elements or just as fills and backfills. In the next part of the revivew, the methodology and selected results of shrinkage tests on concrete composite samples with the addition of various amounts of additives and price tests to reference samples without dispersed reinforcement are presented and discussed. Research has been carried out on the subject of balance between concrete and the semi-finished product used.

Calculation method steel reinforced concrete continuous bridge spans with two reinforced concrete slabs on the effect of concrete shrinkage

The article is considered calculation method steel reinforced concrete continuous bridge spans with two reinforced concrete slabs on the effect of concrete shrinkage. For long-term processes that must be considered when calculating the span structures of bridges, besides creep, concrete shrinkage applies. Object of study: composite steel and concrete span beam bridge with two reinforced concrete slabs. Purpose: to develop a calculation method the cross section steel reinforced concrete bridges with two reinforced concrete slabs on the effect of concrete shrinkage considering concrete creep. Continuous spans of steel reinforced concrete bridges with two reinforced concrete slabs over intermediate supports much more economically, in terms of metal consumption, compared to steel reinforced concrete bridges with one concrete slab. Cross section of a reinforced reinforced concrete beam consists of a steel part that combined with two reinforced concrete slabs. The article presents the results of the calculation of continuous steel-concrete superstructure of a road bridge with two reinforced concrete slabs by the above method.