If the employer believes that changing the shape, quality, or quantity of the work or some part of it is appropriate, he has the authority to order the contractor to do so. These instructions would extend the time it takes to accomplish the task and, as a result, the project's completion time. In the majority of situations, the employer and the contractor couldn't agree on how to compute the extra time the contractor was provided as a result of change orders. The aim of this research is to find a mechanism to determine the additional time required to carry out these works, which will vary based on the type of work, the increase in quantity for any work within the contract, etc.. Modify the nature, quality or type of any work, change the levels, lines, position and dimensions of any part of the work, and perform any additional work necessary to finish the works. A field visit and survey will be conducted on the various bridge projects as part of the research to determine the types of change orders and the additional time required for each of them, in addition to the most important reasons for not using the relative change length and how each project differs from the other. Mathematical software can be enhanced to reliably calculate the additional time for each form of change order. Most of the works expected to appear in variation order are steel and concrete works, and asphalt cladding works, with a frequency of each of them (25 percent), followed by excavation works, which have a frequency of (16.66 percent) in bridge projects.
This study addressed some important tests for concrete including thermal, acoustic insulation and some mechanical behaviour of concrete containing granular Polyvinyl Chloride (PVC) waste as a sand replacement. The PVC waste was collected from a plant of manufacturing PVC doors and windows, was used to replace some of fine aggregate at ratios of 2.5%, 5%, 7.5%, 10%, 12.5% and 15% by weight Properties that studied are thermal conductivity, acoustic insulation slump, fresh density, dry density, compressive strength, flexural strength, and splitting tensile strength. Curing ages of 7, 28, and 56 days for the concrete mixtures were applied in this work. From the results of this study, it is suggested that using of 12.5% fine PVC as a sand replacement by weight can improve thermal insulation to about 82.48% more than concrete without plastic waste Acoustic insulation is about 43.09% more than reference mix and it satisfies the requirement of ACI 213R 2014 for structural lightweight concrete.