State of the Art Review of Reinforcement Strategies and Technologies for 3D Printing of Concrete

This state of the art review paper aims to discuss the results of a literature survey on possible ways to reinforce printed concrete based on existing reinforcement strategies. Just as conventional concrete, for 3D printed concrete to be suitable for large-scale construction, reinforcement is needed to increase the tensile capacity of concrete members and reduce temperature and shrinkage cracking. Despite efforts that are currently underway, the development of proper reinforcement suitable for printed concrete is still very active on the research agenda. As an initial step for designing suitable reinforcement for printed concrete, the existing reinforcement methods for printed concrete as well as conventional cast concrete from the literature are reviewed and summarized. Through the preliminary evaluation of the suitability and effectiveness of various reinforcement methods, guidelines are proposed to better understand possible solutions to reinforce printed concrete and inspire new practical ideas to fill the current technology void. The conclusions also include the possible improvements of the existing reinforcement methods to be considered in future applications.

Development of a Practical Heat of Hydration Model for Concrete Curing for Geotechnical Applications

Thermal integrity profiling (TIP) is a common non-destructive technique to evaluate the quality of construction of piles by analysing the temperature fields due to heat of hydration from freshly cast concrete piles. For this process to be accurate, a reliable concrete heat of hydration model is required. This paper proposes a practical and simple to calibrate four parameter model for the prediction of concrete heat of hydration. This model has been shown to be able to reproduce the evolution of heat of hydration measured in laboratory tests, as well as field measurements of temperature within curing concrete piles, as part of a thermal integrity profiling (TIP) operation performed at a site in London. With the simplicity of the model and the small number of model parameters involved, this model can be easily and quickly calibrated, enabling quick predictions of expected temperatures for subsequent casts using the same concrete mix.

Experimental Study of the Effect of Cavities on the Load Capacity of Two-Way Reinforced Concrete Plates on Fixed Concrete Thickness

The study aims to determine the effect of cavities on the load capacity of reinforced concrete slabs when compared to massive reinforced concrete slabs that have the same thickness, with the hope of reducing the structure’s weight and the use of concrete materials. The modified PVC pipes, as cavity formers, will be placed in the tensile area without reducing the flexural strength that is caused by the weak nature of concrete against tensile strength. The test is carried out on a full scale against 14 cm thick solid plates (PP-1), and hollow plates, which use modified PVC pipes (PB-2), with a cavity diameter of 7.6 cm that has the same thickness. The test uses joint supports on all four sides and the loading pattern is evenly distributed. All slabs are made, on the spot, of cast concrete with the same size and distance between the reinforcement. PVC hollow plate (PB-2) has the same effective thickness as solid plate but has 14% less concrete volume. The maximum load capacity on the solid plate (PP-1) is 522.66 kN and on the hollow plate (PB-2) is 444.33 kN. The melting capacity on the solid plate (PP-1) is 373,515 kN and on the hollow plate (PB-2) is 325,935 kN. Initial crack load capacity on the solid plate (PP-1) is 19.5 kN and on the hollow plate (PB-2) is 16.75 kN

Case study of fungal growth on newly cast concrete floors

In several cases, the Danish Technological Institute has experienced widespread fungal growth on newly cast concrete floors, with a moisture barrier and floating wooden flooring. The reason for fungal growth is usually due to an inadequate drying period. Existing recommendations require that the relative humidity (RH) of air in equilibrium with the concrete, measured in the middle of the concrete, should not exceed 85-90% RH. In this study, six randomly picked apartments in a newly built apartment complex, were chosen for a case study of fungal growth and moisture on newly cast concrete. The study demonstrates that at least some pecies of fungi can grow very well on newly cast concrete if the surface is dusty and moist. The study also demonstrates that a few samples on the surface will often be representative for the whole floor. The study finds that there is a need to revise the existing guidelines for acceptable moisture content in the concrete before mounting the floor. This might have an impact on the entire building process and/or the design of the floor construction. The study also finds that there is a need for a guideline for measuring moisture and fungal growth on newly cast concrete floors.

Centrifugally-cast concrete poles with non-metallic reinforcement

The article describes the testing of poles for electric power transmission lines, which are made of centrifugally-cast concrete and ultra-high strength concrete, and which are prestressed with Carbon Fibre Reinforced Polymer tendons (CFRP). The presented results of pole ultimate load testing suggest the potential for usage of this construction product, particularly in aggressive environments with high probability of steel corrosion. Part of the tested poles had shear reinforcement in the form of confined Glass Fibre Reinforced Polymer (GFRP) grid, while one share of samples had no shear reinforcement, but the concrete matrix was strengthened with synthetic macro fibres. A review is given on similar product testing, calculation methods, and guidance is provided for further research.

RESEARCH OF STRESS CONCRETE CONSTRUCTION AND TECHNICAL PROPERTIES AFTER THERMAL PROCESSING

Строительно-технические свойства бетонов, используемых для замоноличивания стыков конструкций, имеют важное значение. С увеличением водоцементного отношения расширение бетонных образцов во время обогрева возрастает по величине и уменьшается по продолжительности своего развития. Обогрев в условиях частично-исключенной массоотдачи интенсифицирует расширение и рост прочности, а тепловые процессы закрепляютрасширяющуюся структуру. К бетону заделки стыков конструкций предъявляются определенные требования по плотности, так как бетон заделки несет также функции антикоррозийной защиты. Предварительное выдерживание напрягающего бетона в нормальных условиях до его термообработки позволяет набрать необходимую прочность. Выполненные опыты показали, что сцепление арматуры с напрягающим бетоном несколько выше чем с обычным бетоном. С увеличением водоцементного отношения и температуры изотермического выдерживания величина сцепления арматуры с бетоном после его термообработки снижается. Замоноличивание стыков предусматривает использование литых бетонных смесей, что дает возможность применения суперпластификаторов. Их присутствие снижает электрическое сопротивление бетонной смеси и увеличивает водоудаление. Важной является проблема морозо и водостойкости бетонов стыков, связанная с обеспечением его долговечности. Результаты проведенных исследований показали достаточную морозостойкость и водонепроницаемость напрягающего бетона для обеспечения эксплуатации замоноличенных стыков конструкций. The construction and technical properties of concrete used for monolithic joints of structures are important. With an increase in the water-cement ratio, the expansion of concrete samples during heating increases in magnitude and decreases in duration of its development. Heating under conditions of partially-excluded mass transfer intensifies the expansion and growth of strength, and thermal processes fix the expanding structure. Concrete sealing joints of structures are subject to certain density requirements, since concrete sealing also carries the functions of corrosion protection. Preliminary exposure of tensile concrete under normal conditions to its heat treatment allows you to gain the necessary strength. The performed experiments showed that the adhesion of reinforcement with tensile concrete is not much higher than with ordinary concrete. With an increase in the water-cement ratio and the temperature of isothermal aging, the adhesion of the reinforcement to concrete after its heat treatment decreases. The monolithization of joints involves the use of cast concrete mixtures, which makes it possible to use superplasticizers. Their presence reduces the electrical resistance of the concrete mix and increases water removal. An important problem is the frost and water resistance of concrete joints, associated with ensuring its durability. The results of the studies showed sufficient frost resistance and water tightness of the straining concrete to ensure the operation of monolithic joints of structures.

Study of the influence of modern superplastificators on the properties of road cement concrete

In the technology of road concrete, the use of plasticizing additives is mandatory. In the last century, the most widely used plasticizers are lignosulfonates. These additives reduce the water demand of concrete mixtures by 10...15 % and increase the strength of concrete by 20...25 %. However, the presence of sugars in their composition leads to a strong slowdown of the hardening processes and can lead to a decrease the strength of concrete at the age of 28 days. In this century, modern superplasticizers based on polycarboxylates began to be widely used in industrial and civil construction. They were mainly used for the manufacture of cast concrete mixtures. On the other hand, their use in moderately mobile concrete mixes allows reducing water demand by 35...40 % and increasing strength by 60...100 % compared to concretes without additives. However, in such mixtures the use of polycarboxylates leads to a quick setting of the ce-ment and an accelerated set of concrete strength. This does not meet the requirements of the road concrete standards. The goal of the work is to study the influence of modern chemical additives of various nature on the basic properties of road cement con-crete. The article is devoted to the actual problem of the effective use of polycarboxylate superplasticizers

Flexural Behavior of 3D printed Concrete Beam with Fiber Reinforcement

3D printing with concrete is a promising new method for rapid, low cost construction. The flexural strengths for reinforced/unreinforced and 3D printed/cast concrete Warren trusses were tabulated and the failure mechanisms were reported. The types of reinforcement used were rebar(basalt and steel), and mesh (basalt and aramid). The effect of loading geometry and loading speed was measured for basalt mesh and aramid mesh composite, respectively. Due to the expected variation in flexure between samples, it cannot be said whether small differences for various tests are significant. Variation stems from a microscopically uneven surface and random inhomogeneities in the bulk of the tested material which act as a microcrack catalyst and propagator. Since the tested beams are short specimens the numerical findings of other studies will vary based on the intended design. This paper is intended to assess the performance of various reinforcements in a qualitative sense by comparing basalt reinforcement with other reinforcements. It was found that cast beams tolerated deflection better but had a similar flexure strength compared as the printed beams. The steel and basalt rebar reinforced beams had the highest flexure strengths where the traditional steel rebar reinforcement outperformed the basalt in flexure by 36% and the basalt outperformed the steel in deflection by 40%. The basalt mesh outperformed the cast and printed unreinforced bars by a small margin but had only 25% of steel rebars’ deflection at maximum flexure strength. The aramid mesh tolerated the biggest deflection out of any sample at 2.26 cm.