Additive manufacturing in construction is beginning to move from an architect"s modelling tool to delivering full-scale architectural components and elements of buildings such as walls and facades. This paper discusses large-scale additive manufacturing processes that have been applied in the construction and architecture arena and focuses on "Concrete Printing", an automated extrusion based process. The wet properties of the material are critical to the success of manufacture and a number of new criteria have been developed to classify these process specific parameters. These criteria are introduced and key challenges that face construction scale additive manufacturing are presented.

This paper presents the experimental results concerning the mix design and fresh properties of a high-performance fibre-reinforced fine-aggregate concrete for printing concrete. This concrete has been designed to be extruded through a nozzle to build layer-by-layer structural components. The printing process is a novel digitally-controlled additive manufacturing method which can build architectural and structural components without formwork, unlike conventional concrete construction methods. The most critical fresh properties are shown to be extrudability and buildability, which have mutual relationships with workability and open time. These properties are significantly influenced by the mix proportions and the presence of superplasticiser, retarder, accelerator and polypropylene fibres. An optimum mix is identified and validated by the full-scale manufacture of a bench component.

10 11 12This paper presents the hardened properties of a high-performance fibre-reinforced 13 fine-aggregate concrete extruded through a 9 mm diameter nozzle to build layer-by-14 layer structural components in a printing process. The printing process is a digitally 15 controlled additive method capable of manufacturing architectural and structural 16 components without formwork, unlike conventional concrete construction methods.

The application of the concept of circular economy thinking in construction, which is in its infancy, has been largely limited to construction waste minimisation and recycling. Little research on circular economy from a systems perspective including how new business models might enable materials to retain high residual values has been undertaken. Utilising the results from a survey and a follow-up workshop, this paper provides an analysis of an industrywide perspective of circular economy awareness, challenges and enablers. The survey results indicate that while there is industrywide awareness of the concept, clients, designers and subcontractors are the least informed and this is a key challenge for greater adoption. The absence of incentives to design products and buildings for disassembly and reuse at their end of life is a significant challenge. To encourage greater implementation of circular economy principles throughout the supply chain, a clear economic case is paramount, supported by metrics, tools and guidance.

Traditionally businesses have measured their performance solely in financial terms. This limited approach has been challenged, with the introduction of the concept of key performance indicators (KPIs) for non-financial results. In response to the Latham and Egan Reports, the UK construction industry has developed its own set of KPIs. However, their effective use has been limited. This paper reviews these and other construction KPIs and concludes that most of the KPIs used are post event, lagging measures that do not provide the opportunity to change. Their results are not validated and thus are open to interpretation. The result is that KPIs are being used within the industry as a marketing tool, and not as an integral part of business management. This paper distinguishes between three types of measure and suggests a framework for their effective use within an overall performance measurement system based on change action driven by results.The industry must replace competitive tendering with long term relationships based on clear measurement performance in quality and efficiency . . . [by] producing its own structured, objective performance measures agreed with clients . . . Construction companies must prepare