“Dear Ai Weiwei, You have applied for a sixmonth business visit visa, but on this occasion your visa has been restricted,” reads a letter to the artist from the Beijing British Embassy, photographed and posted to his Instagram account. There’s a grotesque irony in the reality of the reason given for his visa restriction being an undeclared “criminal conviction” in China: his 81-day detention for crossing “the red line of Chinese law” is traumatically depicted in S.A.C.R.E.D. (2012), the penultimate piece in the very RA exhibition which prompted his UK visa application.

The viewer is confronted with six identical black cuboids, each with two windows. Because of the tremendous popularity of the exhibition, you have to wait in line to look through them, winding your way past pushchairs and school parties. Inside each one is a painstakingly accurate fi breglass diorama, drenched in bright, white light. Fibreglass Ai Weiwei is scrutinised at close proximity by two guards, and looking from above or from the side, we scrutinise them both.

And yet there’s so much more here than the new surveillance of shifting of the viewer’s gaze, or the irony of the installation’s situation. This is more than a catharsis or a mockery; in S.A.C.R.E.D., basic human rituals of eating, sleeping, and washing are laid (quite literally) bare in hyper-realistic form. The repetition from each scene to the next is a stark inversion of the mundanity of these human rituals: their bleak ‘Sacrament’ is an uncanny anti-sacredness. The paradoxical permanence of these statuesque Doppelgängers and the cruel monotony of the unchanging, white room are in constant tension with the movement tracked from diorama to diorama. Weiwei’s 81, unchanging days are crystallised, monumental, and perverted in S.A.C.R.E.D.– you even see him on the toilet.

Permanence and change wrestle time and time again throughout Weiwei’s output, most infamously in his triptych ‘Dropping a Han Dynasty Urn’ (1995) and accompanying “appropriation” of similar vases, which he has painted in vivid colours. One, bright red, bears the Coca Cola logo. Some critics have tritely dismissed these intensely political gestures as “posturing”, but Weiwei’s harsh comments on the Western fetishisation of ancient Chinese arts, their high monetary values in conflict with Chinese authorities’ seeming lack of care for them, are just one facet of his work with dynasty vases. Here, his activism collides with a snapshot of the split second before the smash, the “vandalistic”, irreversible re-painting of ancient artefacts which once seemed so permanent. These are serious engagements with serious questions about the nature of the work, and the results are both shocking and devastating: in his seeming destruction, he has made something new.

Nevertheless, the garishly post-modern confrontation of the vases is in some way a disappointment after his Qing Dynasty ‘Stool’ and ‘Table with Two Legs on the Wall’ (1997) three rooms earlier. These pieces of seamlessly re-imagined furniture ask all of the same questions as the vases, but the more elegant fi gures that they cut are testament not only to Weiwei’s interrogative approach, but his immensely effective commissioning of traditional woodwork techniques. The sense of entrapment is achieved by the legs literally pressing against the wall, making another floor of it and de-centering the entire room; in ‘Grapes’ (2010), it’s impossible to see where one antique stool ends and another begins.

In his manipulation of mundane furniture forms, Ai Weiwei renders them useless: how do you eat off a table with a fi ve-metre pillar protruding through it? How do you sit on a chair with a tree embedded in it? His “useless objects” are more of the mundane (an armchair, a pushchair,) with added sexuality (anal beads, a butt plug,) and threat (a gas mask, handcuffs, CCTV cameras on the staircase.) In an invocation of permanence strikingly similar to that of Anselm Kiefer’s enormous lead books displayed at the RA this time last year, the “useless objects” are carved out of marble. Yet unlike Kiefer, Weiwei’s mockery of these flagrantly mundane objects sees a traditional Chinese building material transformed into the whitewashed workaday. In the final piece, Weiwei inverts this process, starting with a mundane building material and creating a vast centrepiece. ‘Bicycle Chandelier’ (2015,) as the name suggests, is constructed from China’s most ubiquitous mode of transport. The common bicycle is fragmented and repeated to create towering columns and beautifully imposing geometric tunnels. To be brutally frank, the softer decadence of the white-and-gold sloped plaster ceiling of the RA sort of spoils it.

Weiwei’s most moving transformation at the RA this winter, however, weighs heavily on the gallery floor. 90 tonnes of reinforced steel rods make up the matter of ‘Straight’ (2008-12). For the most dramatic of Weiwei’s “found object” installations, each of these rods were gathered in the wake of the devastating Sichuan earthquake of 2012, hammered straight over several years by a team of six, and painstakingly laid into a vast, undulating, tectonic landscape on the floor. The walls of the gallery are lined with the names of children who died at school during the quake, crushed by their poorly constructed classrooms, many of their deaths unrecognised by Chinese authorities. Along with the screams and cries of the aftermath footage in Weiwei’s film Little Girl’s Cheeks (2008) which plays in the same room, this staggeringly large grid of names forms a harrowing background to a work of such astonishing proportions and beautifully controlled form, as it tapers off at each end. Within the trauma glaring out of each of the four walls, there is something powerfully moving and cathartic conveyed by this landslide of straight metal lines.

The pace of this exhibition is relentless. Between the dissident and the devastating, the ancient and the new, the moving and the funny, there is a constant discussion here and it is anything but dull or flippant. For a handful of weeks this winter, London’s grinding streets held a few rooms full of uselessness, and each one was bold, beautiful and strange.