Keller has reported pre-tax profits of £26.8m for the six months to 30 June 2013, before exceptional items, up from £11.0m for the same period last year.
Revenue was up 5% to £644.6m, from, £613.8m last time.
Chief executive Justin Atkinson said: "This is a much improved first-half performance, with three out of four of the group's divisions significantly more profitable than in the same period last year.
"We expect revenue in the second half to be broadly flat year on year, after adjusting for the effect of acquisitions. However, through careful contract selection and further benefit from our business improvement initiatives, we also expect to report an improved margin, taking us closer towards our 6% target.
"Accordingly, the group's results for the full year are expected to be towards the top end of current market expectations."