Concrete Overstrength: Assessment of Field Strength Seeking Insights for Overdesign Optimization

This study investigates the high contents of cementitious materials in Portland cement concrete and assesses the required (f’cr) and actual (σ) compressive strength of concrete specimens. A linear optimization technique identifies the required binder content to reach f’cr. Standard specifications have required concrete overdesign (OD) for decades, but few studies have evaluated the actual magnitude of OD from field data. The compressive strength of 958 cylinders prepared in the field represented 8200 m3 of ready-mixed concrete with 300 and 450 kg/m3 of cementitious are analyzed. The actual OD appears to be 7 to 21% higher than required. The required 28-day compressive strength of concrete was achieved in less than seven days. Therefore, the content of the cementitious materials could be reduced by 6 and 17% so that concrete could reach f’cr without cementitious overconsumption. Reducing cementitious content is recommended to improve construction quality and optimize resource utilization. Among the main reasons for this recommendation are the estimated substantial long-term savings, increased concrete durability and more rational use of natural resources required to build the structures.

Effects of 0-30% Wood Ashes as a Substitute of Cement on the Strength of Concretes

To fight against the high cost and the increasing scarcity of cement and at the same time to reduce the CO2 greenhouse gases emission associated with the production of Portland cement, two types of wood ashes as a substitute of cement in the production of concretes were investigated. In this paper, we substituted cement by two types of species of wood ashes namely, avocado and eucalyptus ashes following the proportions ranging from 0% to 30 % on one hand, and on the other hand, we added these two types of species of wood ashes namely, avocado and eucalyptus ashes following the proportions ranging from 0% to 10 % by weight of cement in the concrete samples. After 7, 14 and 28 days of curing, compressive strength tests were conducted on these concrete samples. The findings revealed that using wood ashes as additives/admixtures or as a substitute of cement in the production/manufacturing of concrete decreased the compressive strength of concrete. Hence, it can be said that wood ash has a negative influence on the strength of concrete. At three percent (3%) and ten percent (10%) of addition, the wood ash from eucalyptus specie offers better resistance compared to the wood ash from avocado specie, whereas at five percent (5%) of addition, the wood ash from avocado specie offers better resistance compared to the wood ash from eucalyptus specie. At thirty percent (30%) of substitution, the wood ash from eucalyptus specie offers better resistance compared to the wood ash from avocado specie. The compressive strengths increase with the increase of curing age.

Research on Shrinkage Inhibition Technology of C50 Steel Shell Immersed Tube Self-Compacting Concrete

The effects of shrinkage reducing agent and expansion agent on workability, strength and shrinkage of C50 self-compacting concrete with steel-shell immersed tube were studied. It is found that the expansive agent can increase the 28d compressive strength of concrete and restrain the shrinkage of concrete, but it can reduce the mixture property of concrete, and the shrinkage reducing agent can reduce the 28d compressive strength of concrete, but it can obviously restrain the shrinkage of concrete and improve the performance of concrete mixture. On the basis that the performance of concrete mixture meets the technical index, when the dosage of shrinkage reducing agent is 1.5%, the performance of concrete mixture is the best, and the drying shrinkage rate of 28d is the smallest. At this time, the properties of C50 steel-shell sunk pipe self-compacting concrete are as follows: slump flow 720mm, T50 2s, pour-down time 2s, v-shaped funnel passing time 6s, 28d compressive strength 59.6 MPa, 28d drying shrinkage 135×10−6.

Estimation of Present-Day Strength of Concrete for a 40-year-old Building from Non-destructive Tests: A Case Study "

Assessment of the present health of existing concrete structures is necessary, particularly for enhancing the life of the infrastructure facilities reaching the end of their design life. The codes stipulate establishment of site-specific correlation expressions to estimate the compressive strength of concrete from indirect non-destructive tests (NDT) such as rebound hammer or ultrasonic pulse velocity tests. However, in certain circumstances, requisite number of partially destructive (core) tests required for establishing the site-specific equations might not be feasible. In such scenario, selection of a suitable correlation expression from literature has to be performed in a rational way, as discussed in this article with a case study of a 40-year-old concrete building. From the study, it has been ob-served that for the limited number of direct tests, the Indian code stipulation resulted in higher characteristic strength of concrete as compared to the parametric estimation, which can be attributed to the assumption of Normal distribution and code stipulated (conservative) standard deviation value. In case of the indirect estimation cases, the parametric characteristic strength was pretty close to the corresponding non-parametric values indicat-ing that the fitted distributions represented the strength values very well. Recommendations for the suitable cor-relation expression from literature applicable for estimation of equivalent strength from NDT for the structure, recommendation for characteristic compressive strength of concrete and the suggestions for accounting for the inaccuracies in estimated strength in subsequent structural re-analysis have been provided from the results of the study.

Size effect at testing strength properties of concrete

Various strength characteristics of concrete are considered as fracture parameters. The compressive strength of concrete is of paramount importance when designing concrete structures, whereas tensile strength of concrete is the basic property when estimating cracking resistance of a structure and analysing fracture processes in concrete. When testing the compressive strength of concrete, the results are dependent on the shape and dimensions of used specimens. Some findings reported in the literature suggest that size effect exists also when testing such fracture properties of concrete as tensile strength. Unfortunately this problem is much less recognized and described compared to size effect in compressive test results. In this paper, the experimental investigation is presented on how the length of cylindrical specimens influences the tensile splitting strength of concrete obtained by means of the Brazilian method. Additional variable parameters were: type of aggregate (natural gravel and crushed granite) and cement-water ratio (C/W = 1.8 and C/W = 2.6). In conducted laboratory experiments a higher splitting tensile strength of concrete was noted for all specimens with nominal dimensions of 150×150 mm, compared to specimens 150×300 mm in size, regardless of type of aggregate or cement-water ratio.

RECYCLE GLASS WASTE AS A REPLACEMENT OF FINE AGGREGATE IN CONCRETE MIX STANDARD COMPARISON

Recycling is one way that is used to minimize the amount of waste that exists. Recycling is also a process to reduce the use of new raw materials, reduce energy use, reduce pollution, land degradation and greenhouse gas emissions. Materials that can be recycled consist of waste of glass, plastic, paper, metal, textiles and electronic goods. Glass has characteristics suitable as concrete aggregates, considering that glass is a material that does not absorb water. In addition, glass has high abrasion resistance. Meanwhile, the waste glass flux lowers the temperature to the temperature at which the formers will melt. Stabilizers in glass waste are made of calcium carbonate, which makes the glass waste solid and water-resistant. This glass waste is recycled by mixing it into the concrete mix. The recycling method is done by pounding the glass and putting it into the concrete mix stage. The purpose of mixing the glass waste is expected to increase the compressive strength of concrete. The use of glass waste as a mixed material affects the compressive strength of the concrete. The concrete with the most inferior to highest compressive strength is 4% variation concrete, 2% variation concrete, and traditional concrete. Optimal percentage addition of glass waste impacts on maximum concrete compressive strength is 2% mixture variation which obtained 11,88 Mpa & 11,32 Mpa.

THE EFFECT OF ADDING CEMENT WASTE ON THE QUALITY OF CONCRETE COMPRESSIVE

Infrastructure development is one of the important aspects of the progress of a country where most of the constituents of infrastructure are concrete. The most important constituent of concrete is cement because its function is to bind other concrete materials so that it can form a hard mass. The large number of developments using cement as a building material will leave quite a lot of cement bags.In this study, the authors conducted research on the effect of adding cement waste to the compressive strength of concrete. This study used an experimental method with a total of 24 test objects. The test object is in the form of a concrete cylinder with a diameter of 15 cm and a height of 30 cm and uses variations in the composition of the addition of cement waste cement as a substitute for fine aggregate, namely 0%, 2%, 4% and 6%. K200). The compressive strength test was carried out at the age of 7 days and 28 days.The test results show that the use of waste as a partial substitute for fine aggregate results in a decrease in the compressive strength of each mixture. at the age of 7 days the variation of 2% is 16.84 MPa, 4% is 11.32 MPa and for a mixture of 6% is 6.68 MPa. Meanwhile, the compressive strength test value of 28 days old concrete in each mixture decreased by ± 6 MPa. So the conclusion is cement cement waste cannot be used as a substitute for fine aggregate in fc 16.6 (K200) quality concrete because the value is lower than the specified minimum of 16.6 MPa.

Workability dan Sifat Mekanik Self Compacting Geopolimer Concrete (SCGC)

The purpose of this study was to investigate the relationship between molarity and workability in Self-Compacting Geopolymer Concrete (SCGC), as well as mechanical properties. Compressive strength and split tensile strength tests are used to characterize the mechanical characteristics in this research. Additionally, the study investigates the optimal molarity for self-compacting geopolymer concrete. Fly ash was used in lieu of cement in this research. On new concrete self-compacting geopolymer, workability is determined using the EFNARC standard, which includes the Slump Flow, V-Funnel, and L-Box tests. ASTM 39/C 39M-99 standard is used to determine the compressive strength of self-compacting concrete geopolymer. On new concrete, workability is determined using the EFNARC standard, which comprises the Slump Flow Test, a V-funnel, and an L-Box. The compressive strength of concrete samples is determined according to the ASTM 39/C 39M – 99 standard. The SNI 03-2491-2002 standard is used to determine the split tensile strength of concrete. At the ages of 7, 14, and 28 days, tests were conducted. The findings indicated that new concrete at 11M-13M satisfied the criteria for SCGC workability. The compressive and split tensile strengths of SCGC grow as the concrete ages. In self-compacting geopolymer concrete, the optimal molarity is 13 M.