•The first large-scale field trial of microcapsule-based self-healing concrete in the UK.•Microcapsules were developed and implemented in concrete on site.•Self-healing process was demonstrated both ...in field and laboratory assessment.•Crack width and depth and permeability reduction and strength recovery was achieved.
Maintaining the health and reliability of our infrastructure is of strategic importance. The current state of the UK infrastructure, and the associated huge costs of inspection, maintenance, repair and eventual replacement, is not sustainable and is no longer environmentally viable. The design of infrastructure, mainly concrete, remains traditional and poor material performance continues to be the main cause of deterioration and failure in our infrastructure systems. Biomimetic materials, that emulate natural biological systems in their ability to self-healing, provide an exciting and plausible solution. Embedding cementitious materials with in-built capabilities to sense and respond to their environmental triggers could potentially eliminate all external interventions and deliver a resilience infrastructure. The work presented in this paper forms part of a national initiative that has been developing biomimetic cementitious infrastructure materials which culminated in the first large-scale field trials of self-healing concrete in the UK testing four different but complementary technologies that were developed. This paper focuses on one self-healing technology, namely microcapsules, which contain a healing agent that is released on their rupture as a result of crack propagation. The paper will present details of the microcapsules used, their implementation in concrete and in the field trials and time-related, field and laboratory, assessment of the self-healing process. It also highlights challenges faced and improvements that are now on-going to produce the next generation of the microcapsule self-healing cementitious system.
This paper presents research on the response and behavior of both high strength concrete (107 MPa) and normal strength concrete (27.6 MPa) slabs doubly reinforced with high strength low alloy ...vanadium (HSLA-V) reinforcement (VR) and conventional steel reinforcing bars (NR) subjected to explosive loads. Four types of reinforced concrete (RC) slabs namely High Strength Concrete (HSC) with HSLA-V Steel Reinforcing bars (HSC-VR), High Strength Concrete with Conventional Steel Reinforcing bars (HSC-NR), Normal Strength Concrete (NSC) with HSLA-V Steel Reinforcing bars (NSC-VR), and Normal Strength Concrete with Conventional Steel Reinforcing bars (NSC-NR) have been studied and compared both experimentally and numerically. The slabs were subjected to blast loads using a shock tube capable of generating both positive and negative phase pressures. Data collected during the dynamic experiments consisted of reflected pressure obtained from several pressure gages arranged along the perimeter of the test article and mid-span deflections captured from an accelerometer, a laser device, and high speed video. The numerical analysis was performed with the commercial program LS-DYNA using two material models. The concrete material models considered were Winfrith Concrete Model (WCM) and Concrete Damage Model Release 3 (CDMR3). Results from the numerical simulation are compared with the experimental values to determine material parameters and other finite element model related constraints. Mesh sensitivity and crack propagation studies were also conducted. From this study it was observed that CDMR3 and WCM can be used over a wider range of concrete compressive strengths. The advantages and disadvantages of using high strength materials are discussed.
•Experimental data from uniform blast loading on doubly reinforced concrete slabs presented.•Comparison of performance of combination of slabs made of high strength concrete and steel.•Finite element analysis using two concrete models in LSDYNA gave good comparison with deflection data.•High strength concrete was very effective in reducing the level of response.•Default material models with default properties can be used to reasonably predict the response of such slabs.
•Statistics on the mechanical properties of concrete with and without recycled aggregates.•Full recycled aggregate incorporation has little effect on the variability of the properties tested.•Normal ...distributions suited all properties of the 12 mixes tested.•Intermediate incorporation ratios increased the concrete’s variability.•Other’s statistics on the properties of natural aggregate concrete agree with our results.
Research on the variability of the properties of recycled aggregate concrete is lacking and is necessary for the development of reliability analyses and code calibration procedures. This paper presents an experimental programme on the within-batch variability of the compressive strength, Young’s modulus, and splitting tensile strength of several recycled and natural aggregate concrete mixes. The influence of the recycled concrete aggregates on the mechanical properties and variability of concrete is analysed and discussed and benchmarks with standard predictions for the variability of natural aggregate concrete are made. It was found that full recycled aggregate concrete incorporation did not increase the variability of any of the properties tested, but intermediate ratios of recycled aggregate incorporation did. The properties of high-strength concrete mixes were more variable than that of all other mixes, irrespective of recycled aggregate incorporation. All properties of all compositions were suitably modelled by normal distributions. The coarse recycled aggregates were sourced from concrete waste.
The increasing concern for safety and sustainability of structures is calling for the development of smart self‐healing materials and preventive repair methods. The appearance of small cracks (<300 ...µm in width) in concrete is almost unavoidable, not necessarily causing a risk of collapse for the structure, but surely impairing its functionality, accelerating its degradation, and diminishing its service life and sustainability. This review provides the state‐of‐the‐art of recent developments of self‐healing concrete, covering autogenous or intrinsic healing of traditional concrete followed by stimulated autogenous healing via use of mineral additives, crystalline admixtures or (superabsorbent) polymers, and subsequently autonomous self‐healing mechanisms, i.e. via, application of micro‐, macro‐, or vascular encapsulated polymers, minerals, or bacteria. The (stimulated) autogenous mechanisms are generally limited to healing crack widths of about 100–150 µm. In contrast, most autonomous self‐healing mechanisms can heal cracks of 300 µm, even sometimes up to more than 1 mm, and usually act faster. After explaining the basic concept for each self‐healing technique, the most recent advances are collected, explaining the progress and current limitations, to provide insights toward the future developments. This review addresses the research needs required to remove hindrances that limit market penetration of self‐healing concrete technologies.
Self‐healing concrete is a smart concrete designed to manage occurring cracks through the activation of an incorporated mechanism resulting in autonomous healing of cracks. This damage management principle provides the material superior functionality with respect to reduced maintenance and repair requirements, increased service life, and sustainability. This review article elucidates and critically evaluates different (stimulated) autogenous and autonomous healing mechanisms.
•Carbonation of concrete mixes with high incorporation ratios of recycled concrete aggregates (RCA), and/or fly ash (FA).•Sequestration of a high amount of CO2 in concrete, by producing a concrete ...with high rate of carbonation.•Service life of concrete made with high volumes of FA and RCA.
This paper mainly focuses the effect of high incorporation ratios of fly ash (FA) and recycled concrete aggregates (RCA) on the carbonation resistance of concrete. The aim of using high volumes of these non-traditional materials is to decrease the use of natural resources and capture CO2. For that purpose, the carbonation resistance of low- and high-strength concrete mixes produced with various incorporation ratios of FA, fine RCA and coarse RCA, jointly and individually, is obtained and related with compressive strength, water absorption and chloride ion penetration. The results show that the carbonation depth of concrete increased up to 3 and 6 times when incorporating 30% and 60% of FA, respectively, and 100% of RCA led to up to 2.7 times increment. Therefore, the concrete cover for mixes made with FA and/or RCA should be increased in order to obtain an equivalent service life to that of conventional concrete. In spite of this fact, it is recommended to incorporate FA in RCA concrete because, in most concrete mixes, the carbonation depth due to the combined effect of both RCA and FA was lower than the sum of the values due to each effect. Additionally, the results show that, although the carbonation rate of concrete mixes containing high volumes of FA and RCA is high, their service life is also relatively high and the concrete reinforcement can be protected for up to 50 years.
The consumption of various forms of plastics is a challenging environment protection issue. All forms of consumed plastic become waste and require large areas of land for storage because several tons ...of waste plastics cannot be fully recycled at once. The low biodegradability of plastic and the presence in large quantities of waste plastic negatively impact the environment. Previously, various studies were performed to identify safe and environmentally friendly methods for disposing of plastics. Recently, various forms of plastics have been incorporated in concrete to prevent the direct contact of plastics with the environment because concrete has a longer service life. However, this method is not a dominant method for disposing of waste plastic. This paper presents an overview of some published research regarding the use of waste plastic in concrete. The effects of waste plastic addition on the fresh, mechanical and thermal properties of concrete are also presented in this paper.
This paper presents data on the chloride diffusion coefficient (Dcl), ageing coefficient (m) and chloride threshold (Clth) related to seven concrete mixes (four M35 and three M50) with OPC, OPC + PFA ...(pulverised fuel ash) and limestone-calcined clay cement (LC3). Using these, the service lives of a typical bridge pier and girder with the PFA and LC3 concrete were found to be much higher than those with OPC concrete of similar strength. From life-cycle assessment, the CO2 footprint of PFA and LC3 concrete were found to be significantly lower than those of OPC concrete of similar strength. Further, the CO2 emissions per unit of concrete per year of estimated service life, as a combined indicator of service life and carbon footprint, are similar for concrete with PFA and LC3, which are much lower than that with OPC.
•Recycled aggregates were incorporated into mixtures by ratio of 25–30–55%.•Compressive strength between 32 and 43MPa was attained with recycled aggregates.•Optimum fiber content was determined as 1% ...by volume.•The greatest negative impact of RCA was experienced at water penetration depths.•Use of RCA is more suitable at constructions that have low structural risk factor.
In this study, recycling of rubble obtained during urban transformation and manufacturing new concrete using this material was experimentally studied. Different combinations were generated using the recycled concrete aggregates and polypropylene fiber. Natural aggregates were replaced by recycled concrete aggregates (RCAs) and volume of 0%, 1% and 1.5% fiber were introduced for each series. Although concretes’ physical and mechanical properties were affected negatively by RCA due to RCA’s higher porosity and water absorption capacity, high strength concrete was eventually manufactured. Additionally, although fiber content increases flexural properties, there is no significant difference observed between 1% and 1.5%. Percentage contribution ratios of parameters which influence the results of experiments were also calculated by means of analysis of variance (ANOVA) method. As the result of ANOVA which is carried out on specimens containing fiber and recycled concrete aggregate, main factor on changes of compressive strength were determined as aggregate type, while fiber content were also influential on flexural and splitting tensile strength besides aggregate type.
This paper presents an experimental study that investigates the influence of the low fiber content of polypropylene and hooked-end steel fibers on the properties of high-strength concrete. The study ...variables include fiber types and fiber contents. The effect of combining both fibers with a total fiber content of 1.0% was also studied in some mixtures. Silica fume, as a supplementary cementitious material, was used at 10% of the cement weight in all fiber-reinforced concrete mixtures. Compressive strength, modulus of elasticity, longitudinal resonant frequency, rapid chloride migration and free drying shrinkage tests were performed for different curing ages. The results show that replacement of the cement weight with 10% silica fume improved all of the characteristics of the concrete evaluated in this research study. It was observed that the inclusion of fibers, particularly steel fibers, enhanced the mechanical properties of concrete. It was found that the incorporation of polypropylene fibers resulted in a reduction of chloride diffusivity, while introducing steel fibers significantly increased the chloride diffusivity of concrete. Finally, the results showed that hybridization of two types of fibers was an effective way to improve the properties of concrete and specifically reduce the drying shrinkage compared with that of the plain concrete.
•The blast resistant capacities of unbounded bi-directional PSC are experimentally and numerically evaluated.•The blast test procedure and measurement system are established and used to determine ...blast resistance capacity.•The simulation model of prestressed concrete panel under blast loading is calibrated using the test data.•The PSRC members had significantly better blast resistance than RC and PSC members.
In recent years, frequent terror and military attack by explosion and impact have occurred all over the world. Particularly, World Trade Center collapse and US Department of Defense Pentagon attack on Sept. 11 of 2001 and Fukushima nuclear power plant accident due to Northeast earthquake tsunami on the coast of Japan on Mar. 11 of 2011 resulted in devastating human casualties and structural collapses. These terrors and accidents raised public concerns and anxiety of potential structural collapse of major infrastructures and structures. In order to better combat these problems, the extreme loading resistant structural studies are initiated. Among numerous types of target structures, one of the most important structural types is prestressed concrete (PSC), which is widely used for construction of nuclear containment vessel and gas storage tank. In this study, to evaluate the blast resistance and protective capacity of bi-directional PSC member, blast tests were carried out on 1400 × 1000 × 300 mm reinforced concrete (RC), prestressed concrete without rebar (PSC), prestressed concrete with rebar (PSRC) specimens. The applied blast load was generated by detonating 25 kg ANFO explosive charge at 1.0 m standoff distance. The data acquisitions included blast waves of incident pressure, reflected pressure, and impulse as well as behavioral displacements of deflection, acceleration, and strains of concrete, rebar, and PS tendon. Then, the blast test results are used to calibrate finite element simulation model. Once the simulation model is calibrated, it is used to perform parametric study on bi-directional prestressed concrete specimens to further evaluate the blast resistance of the panels. The study results are discussed in detail in the paper.
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