To improve sustainability and reduce the production costs of ultra-high performance concrete (UHPC), the use of locally available aggregates is highly desirable. The combined impact of aggregate type and different supplementary cementitious materials (SCMs) on the fresh and mechanical properties of UHPC is not yet sufficiently understood. Therefore, quartz, limestone, and diabase aggregates together with different SCM combinations were used in the experimental investigation of eighteen UHPC mixtures. Laboratory tests, including flow table, compressive strength, and flexural strength tests, were performed to evaluate the performance of the mixtures. Mixtures containing limestone and fly ash (FA) generally showed higher workability compared to those containing metakaolin (MK). The highest compressive strengths were achieved in mixtures with quartz sand (average 110 MPa) containing approximately 20% MK relative to the total binder content. The mixture with optimal particle distribution and the lowest cement content (500 kg/m3) also showed extremely high mechanical performance. Based on the obtained flexural-to-compressive strength ratios (fb/fc), the expression fc ≈ 7·fb was proposed to estimate the compressive strength of similar fiber-free UHPC mixtures. Furthermore, heat-treated specimens exhibited a 45% higher compressive strength after 7 days compared to the reference mixture, while the addition of polyvinyl alcohol (PVA) fibers caused a slight decrease in compressive strength of approximately 4%. The obtained results contribute to the development of mechanically efficient UHPC mixtures with optimized particle packing and reduced cement consumption, which may improve the sustainability of UHPC production.

This paper provides a research review regarding the creep of ultra-high-performance concrete with or without the addition of fibers. Unlike other similar studies that mainly considered influential factors and their effects on the creep behavior, this research focuses more attention on the analysis of UHPC creep models. For the creep strain assessments of these concretes, the creep models given in the latest standards cannot be used, but it is necessary to modify them to give reliable results, given the rather complex composition of UHPC. Several proposed creep models for UHPC are presented with comparative analysis. The observation is that by varying key parameters such as compressive strength, relative humidity, cross-sectional dimensions, and temperature, there may be major discrepancies between models, so additional experimental investigations are necessary to perform their calibration. In this paper, the parameters α1, α2, and γ of FIB Model Code 2010 have been modified in order to obtain a match with other proposed models in terms of the final value of the creep coefficient and the creep curve. The creep coefficient of the UHPC decreases when steel fiber content increases, but it is important to consider the excessive fiber addition because very often it causes an increase in creep strain. The application of thermal treatment at a temperature of 90 °C for 48 h significantly improves the time-dependent properties of UHPC. An analysis of the impact of the steel fiber content, fiber type, thermal treatment, and the age of the concrete under load on strains of UHPC specimens and beams under long-term loads is performed.

<p style="text-align: justify;">This paper deals with the resistance of the shed of a steel hall in Drvar according to technical regulations for snow from 1961 and EC1 regulations. The paper aims to check the reliability of the shed with probabilistic approach. That also implies calibration of the steel hall construction analyzed with classic deterministic method. Statical system of the shed of a steel hall is a beam with a given span, Figure 1. Steel sections are hot rolled INP sections with specified statistic parameters. The length of the beam span is &lambda; = 2,4 m. The reliability indexes have to be analyzed in point 1(relevant statical forces and displacements for ULS and SLS) and according to equations of limit states.</p>